util: add removedirs as platform depending function

According to fa901423ac23 introducing "windows._removedirs()":

    If a hg repository including working directory is a reparse point
    (directory symlinked or a junction point), then using
    os.removedirs will remove the reparse point erroneously.

"windows._removedirs()" should be used instead of "os.removedirs()" on
Windows.

This patch adds "removedirs" as platform depending function to replace
"os.removedirs()" invocations for portability and safety

mercurial/posix.py

@@ -16,6 +16,7 b' samestat = os.path.samestat'
 oslink = os.link
 unlink = os.unlink
 rename = os.rename
+removedirs = os.removedirs
 expandglobs = False
 
 umask = os.umask(0)

mercurial/util.py

@@ -59,6 +59,7 b' posixfile = platform.posixfile'
 quotecommand = platform.quotecommand
 readpipe = platform.readpipe
 rename = platform.rename
+removedirs = platform.removedirs
 samedevice = platform.samedevice
 samefile = platform.samefile
 samestat = platform.samestat

mercurial/windows.py

@@ -270,7 +270,7 b' def groupname(gid=None):'
     If gid is None, return the name of the current group."""
     return None
 
-def _removedirs(name):
+def removedirs(name):
     """special version of os.removedirs that does not remove symlinked
     directories or junction points if they actually contain files"""
     if osutil.listdir(name):
@@ -297,7 +297,7 b' def unlinkpath(f, ignoremissing=False):'
             raise
     # try removing directories that might now be empty
     try:
-        _removedirs(os.path.dirname(f))
+        removedirs(os.path.dirname(f))
     except OSError:
         pass