tests: fix `hghave root` on windows

tests: fix `hghave root` on windows

This lets tests\test-hghave.t pass on windows where geteuid does not exist.

--- a/tests/hghave.py	Wed Nov 20 12:55:08 2013 +0000
+++ b/tests/hghave.py	Sat Nov 23 01:06:20 2013 +0100
@@ -234,7 +234,7 @@
         os.rmdir(d)
 
 def has_root():
-    return os.geteuid() == 0
+    return getattr(os, 'geteuid', None) and os.geteuid() == 0
 
 def has_pyflakes():
     return matchoutput("sh -c \"echo 'import re' 2>&1 | pyflakes\"",