Avoid crash during rev-parse when the default encoding is ascii

In some locales the default encoding is ascii in which case
subprocess.check_output() will fail if it is given a non-ascii ref as
one of the arguments. By forcing the ref to be utf8 we will avoid a
crash while still behaving correctly when the default encoding is
utf8.

The credits for this fix go to Nikita Bazhinov for discovering the fix
and Chris J Billington for explaining it.

Co-Authored-By: Nikita Bazhinov <nbazhinov@syntellect.ru>
Co-Authored-By: Chris J Billington <chrisjbillington@gmail.com>

hg2git.py

@@ -132,7 +132,8 @@ def get_git_sha1(name,type='heads'):
   try:
     # use git-rev-parse to support packed refs
     ref="refs/%s/%s" % (type,name.decode('utf8'))
-    l=subprocess.check_output(["git", "rev-parse", "--verify", "--quiet", ref])
+    l=subprocess.check_output(["git", "rev-parse", "--verify",
+                               "--quiet", ref.encode('utf8')])
     if l == None or len(l) == 0:
       return None
     return l[0:40]