subrepo: ensure "close()" execution at the end of "_calcfilehash()"

Before this patch, "close()" for the file object opened in
"_calcfilehash()" may not be executed, if unexpected exception is
raised, because it isn't executed in "finally" clause.

This patch ensures "close()" execution at the end of "_calcfilehash()"
by moving it into "finally" clause.

mercurial/subrepo.py

@@ -35,7 +35,9 b' def _calcfilehash(filename):'
     data = ''
     if os.path.exists(filename):
         fd = open(filename, 'rb')
+        try:
         data = fd.read()
+        finally:
         fd.close()
     return util.sha1(data).hexdigest()