hghave: fix hardlink-whitelisted check on Python 3

Differential Revision: https://phab.mercurial-scm.org/D2846

tests/hghave.py

@@ -372,7 +372,7 b' def has_hardlink():'
 def has_hardlink_whitelisted():
     from mercurial import util
     try:
-        fstype = util.getfstype('.')
+        fstype = util.getfstype(b'.')
     except OSError:
         return False
     return fstype in util._hardlinkfswhitelist