Btrfs-progs: Correct path munging in bcp

Bcp was assuming that a path on the command line would never have a slash after
it, which is silly, and would cause the first letter of everything in the root
of the source to be truncated.  Instead, use os.path.relpath to handle
it properly.

Signed-off-by: Carey Underwood <cwillu@cwillu.com>
Signed-off-by: Hugo Mills <hugo@carfax.org.uk>

bcp

@@ -136,8 +136,7 @@ for srci in xrange(0, src_args):
             srcname = os.path.join(dirpath, x)
             statinfo = os.lstat(srcname)
 
-            if srcname.startswith(src):
-                part = srcname[len(src) + 1:]
+            part = os.path.relpath(srcname, src)
 
             if stat.S_ISLNK(statinfo.st_mode):
                 copylink(srcname, dst, part, statinfo, None)
@@ -152,8 +151,7 @@ for srci in xrange(0, src_args):
 
         for f in filenames:
             srcname = os.path.join(dirpath, f)
-            if srcname.startswith(src):
-                part = srcname[len(src) + 1:]
+            part = os.path.relpath(srcname, src)
 
             statinfo = os.lstat(srcname)
             copyfile(srcname, dst, part, statinfo, None)