[BUG] Configuration parser bug when escaping characters

Today I was testing headers manipulation but I met a bug with my first test.
To reproduce it, add for example this line :

    rspadd Cache-Control:\ max-age=1500

Check the response header, it will provide :

Cache-Control: max-age=15000 <= the last character is duplicated

This only happens when we use backslashes on the last line of the
configuration file, without returning to the line.

Also if the last line is like :
  rspadd Cache-Control:\ max-age=1500\

the last backslash causes a segfault.

This is not due to rspadd but to a more general bug in cfgparse.c :
...
if (skip) {
        memmove(line + 1, line + 1 + skip, end - (line + skip + 1));
        end -= skip;
}
...

should be :
...
if (skip) {
        memmove(line + 1, line + 1 + skip, end - (line + skip));
        end -= skip;
}
...

I've reproduced it with haproxy 1.3.22 and the last 1.4 snapshot.
(cherry picked from commit dd1b01d027)

src/cfgparse.c

@@ -3696,7 +3696,7 @@ int readcfgfile(const char *file)
 					}
 				}
 				if (skip) {
-					memmove(line + 1, line + 1 + skip, end - (line + skip + 1));
+					memmove(line + 1, line + 1 + skip, end - (line + skip));
 					end -= skip;
 				}
 				line++;