genosxversion: don't give up if we can't find a path to hg libraries

This doesn't work if you have a PyOxidized hg on $PATH, but everything
is fine if you just ignore that problem.

Differential Revision: https://phab.mercurial-scm.org/D8975

contrib/genosxversion.py

@@ -6,9 +6,14 b' import os'
 import subprocess
 import sys
 
+try:
 # Always load hg libraries from the hg we can find on $PATH.
 hglib = subprocess.check_output(['hg', 'debuginstall', '-T', '{hgmodules}'])
 sys.path.insert(0, os.path.dirname(hglib))
+except subprocess.CalledProcessError:
+    # We're probably running with a PyOxidized Mercurial, so just
+    # proceed and hope it works out okay.
+    pass
 
 from mercurial import util