Check for broken links when updating linkfiles

If a linkfile is a broken link (destination does not exist), and it
needs to be updated, we didn't notice that it needed to be removed
first. Use lexists instead of exists to check for this condition.

Change-Id: I1f6a1f0193d3fd2b9f7a647836044997f6ab32eb

project.py

@@ -249,7 +249,7 @@ class _LinkFile(object):
     if not os.path.islink(absDest) or (os.readlink(absDest) != relSrc):
       try:
         # remove existing file first, since it might be read-only
-        if os.path.exists(absDest):
+        if os.path.lexists(absDest):
           os.remove(absDest)
         else:
           dest_dir = os.path.dirname(absDest)