util: also catch IndexError

This makes life so, so much easier for hgwatchman, which provides a named tuple
but throws an IndexError instead of a TypeError.

mercurial/util.py

@@ -963,7 +963,7 b' def statmtimesec(st):'
     """
     try:
         return st[stat.ST_MTIME]
-    except TypeError:
+    except (TypeError, IndexError):
         # osutil.stat doesn't allow index access and its st_mtime is int
         return st.st_mtime