DOC: fix some spelling issues over multiple files

This is from the output of codespell and may be backported.

INSTALL

@@ -528,7 +528,7 @@ because of strange symbols or section mismatches, simply remove -g from
 DEBUG_CFLAGS.
 
 Building on AIX 7.2 works fine using the "aix72-gcc" TARGET. It adds two
-special CFLAGS to prevent the loading of AIXs xmem.h and var.h. This is done
+special CFLAGS to prevent the loading of AIX's xmem.h and var.h. This is done
 by defining the corresponding include-guards _H_XMEM and _H_VAR. Without
 excluding those header-files the build fails because of redefinition errors.
 Furthermore, the atomic library is added to the LDFLAGS to allow for

doc/configuration.txt

@@ -406,7 +406,7 @@ HAProxy's configuration process involves 3 major sources of parameters :
 
   - the arguments from the command-line, which always take precedence
   - the configuration file(s), whose format is described here
-  - the running process' environment, in case some environment variables are
+  - the running process's environment, in case some environment variables are
     explicitly referenced
 
 The configuration file follows a fairly simple hierarchical format which obey
@@ -1083,7 +1083,7 @@ external-check
   "insecure-setuid-wanted".
 
 gid <number>
-  Changes the process' group ID to <number>. It is recommended that the group
+  Changes the process's group ID to <number>. It is recommended that the group
   ID is dedicated to HAProxy or to a small set of similar daemons. HAProxy must
   be started with a user belonging to this group, or with superuser privileges.
   Note that if haproxy is started from a user having supplementary groups, it
@@ -1756,7 +1756,7 @@ stats maxconn <connections>
   possible to change this value with "stats maxconn".
 
 uid <number>
-  Changes the process' user ID to <number>. It is recommended that the user ID
+  Changes the process's user ID to <number>. It is recommended that the user ID
   is dedicated to HAProxy or to a small set of similar daemons. HAProxy must
   be started with superuser privileges in order to be able to switch to another
   one. See also "gid" and "user".
@@ -14410,7 +14410,7 @@ weight <weight>
 
 HAProxy allows using a host name on the server line to retrieve its IP address
 using name servers. By default, HAProxy resolves the name when parsing the
-configuration file, at startup and cache the result for the process' life.
+configuration file, at startup and cache the result for the process's life.
 This is not sufficient in some cases, such as in Amazon where a server's IP
 can change after a reboot or an ELB Virtual IP can change based on current
 workload.
@@ -20369,7 +20369,7 @@ easier finding and understanding.
           external attacks.
 
      PC   The proxy refused to establish a connection to the server because the
-          process' socket limit has been reached while attempting to connect.
+          process's socket limit has been reached while attempting to connect.
           The global "maxconn" parameter may be increased in the configuration
           so that it does not happen anymore. This status is very rare and
           might happen when the global "ulimit-n" parameter is forced by hand.

doc/internals/htx-api.txt

@@ -113,8 +113,8 @@ payload.
 
 Because the payloads part may wrap, there are 2 usable free spaces:
 
-    - The free space in front of the blocks part. This one is used iff the other
-      one was not used yet.
+    - The free space in front of the blocks part. This one is used if and only if
+      the other one was not used yet.
 
     - The free space at the beginning of the message. Once this one is used, the
       other one is never used again, until a message defragmentation.

doc/intro.txt

@@ -1276,7 +1276,7 @@ HAProxy protects itself against it.
 
 On Linux, a new starting process may communicate with the previous one to reuse
 its listening file descriptors so that the listening sockets are never
-interrupted during the process' replacement.
+interrupted during the process's replacement.
 
 
 3.4.3. Advanced features : Scripting

doc/management.txt

@@ -1986,7 +1986,7 @@ show activity
   of reports of abnormal behaviours. A typical example would be a properly
   running process never sleeping and eating 100% of the CPU. The output fields
   will be made of one line per metric, and per-thread counters on the same
-  line. These counters are 32-bit and will wrap during the process' life, which
+  line. These counters are 32-bit and will wrap during the process's life, which
   is not a problem since calls to this command will typically be performed
   twice. The fields are purposely not documented so that their exact meaning is
   verified in the code where the counters are fed. These values are also reset