posix: disable cygwin's symlink emulation

posix: disable cygwin's symlink emulation

--- a/mercurial/posix.py	Thu Mar 08 20:17:36 2012 +0000
+++ b/mercurial/posix.py	Thu Mar 08 15:59:47 2012 -0600
@@ -277,6 +277,12 @@
     def checkexec(path):
         return False
 
+    # Similarly, Cygwin's symlink emulation is likely to create
+    # problems when Mercurial is used from both Cygwin and native
+    # Windows, with other native tools, or on shared volumes
+    def checklink(path):
+        return False
+
 def shellquote(s):
     if os.sys.platform == 'OpenVMS':
         return '"%s"' % s