Only set mode of new patch if the target file was removed before.

Only set mode of new patch if the target file was removed before.

If the file is writable by the user, but owned by a different user, the
chmod will otherwise fail with "Operation not permitted".

Additionally make very sure that the file is only written if either the number
of links is <= 1 or the file was successfully removed.

Maybe this minimal COW code should be replaced by something from util.

--- a/mercurial/patch.py	Wed Oct 24 22:15:45 2007 +0200
+++ b/mercurial/patch.py	Thu Oct 25 19:40:56 2007 +0200
@@ -9,7 +9,7 @@
 from i18n import _
 from node import *
 import base85, cmdutil, mdiff, util, context, revlog, diffhelpers
-import cStringIO, email.Parser, os, popen2, re, sha
+import cStringIO, email.Parser, os, popen2, re, sha, errno
 import sys, tempfile, zlib
 
 class PatchError(Exception):
@@ -402,11 +402,13 @@
             st = None
             try:
                 st = os.lstat(dest)
-                if st.st_nlink > 1:
-                    os.unlink(dest)
-            except: pass
+            except OSError, inst:
+                if inst.errno != errno.ENOENT:
+                    raise
+            if st and st.st_nlink > 1:
+                os.unlink(dest)
             fp = file(dest, 'wb')
-            if st:
+            if st and st.st_nlink > 1:
                 os.chmod(dest, st.st_mode)
             fp.writelines(self.lines)
             fp.close()