Don't forget to save symlinks pointing to directories

os.walk() yields symlinks to directories in dirnames and do not follow
them. Our backup cycle expects all files that need to go to blob to be
in filenames and that dirnames are only recursed-into by walk().

Thus, until now, symlink to a directory was simply ignored and not
backup'ed. In particular *.git/hooks are usually symlinks to common
place.

The fix is to adjust our xwalk() to always represent blob-ish things in
filenames, and leave dirnames only for real directories.

/cc @kazuhiko

git-backup

@@ -60,7 +60,7 @@ NOTE the idea of pulling all refs together is similar to git-namespaces
 
 import os
 import sys
-from os.path import join as pathjoin, exists as pathexists, dirname
+from os.path import join as pathjoin, exists as pathexists, dirname, islink
 from time import strftime
 from subprocess import Popen, PIPE
 from stat import S_ISLNK
@@ -120,10 +120,18 @@ def xgit(*argv, **kw):
     return stdout
 
 
-# like os.walk() but raise on error + entries are emitted in sorted order
+# like os.walk() but raise on error + entries are emitted in sorted order;
+# symlinks (both to files and directories) are always yielded in filenames
 def reraise(e): raise e
 def xwalk(top):
     for dirpath, dirnames, filenames in os.walk(top, onerror=reraise):
+        # os.walk yields symlinks to dirs in dirnames - move them to files
+        for i, _ in  enumerate(dirnames):
+            if islink(pathjoin(dirpath, _)):
+                filenames.append(_)
+                dirnames[i] = None
+        removeall(dirnames, None)
+
         dirnames.sort();  filenames.sort()
         yield dirpath, dirnames, filenames