py3: fix a type error in hghave.has_hardlink

py3: fix a type error in hghave.has_hardlink

test-hghave.t was failing with:

    feature hardlink failed:  argument 1: <class 'TypeError'>: wrong type

--- a/tests/hghave.py	Fri Sep 21 09:34:41 2018 -0700
+++ b/tests/hghave.py	Fri Sep 21 00:37:03 2018 -0400
@@ -16,6 +16,22 @@
     "false": (lambda: False, "nail clipper"),
 }
 
+if sys.version_info[0] >= 3:
+    def _bytespath(p):
+        if p is None:
+            return p
+        return p.encode('utf-8')
+
+    def _strpath(p):
+        if p is None:
+            return p
+        return p.decode('utf-8')
+else:
+    def _bytespath(p):
+        return p
+
+    _strpath = _bytespath
+
 def check(name, desc):
     """Registers a check function for a feature."""
     def decorator(func):
@@ -360,7 +376,7 @@
     os.close(fh)
     name = tempfile.mktemp(dir='.', prefix=tempprefix)
     try:
-        util.oslink(fn, name)
+        util.oslink(_bytespath(fn), _bytespath(name))
         os.unlink(name)
         return True
     except OSError: