error: derive RevlogError from HintException instead of Exception

This will allow us to now pass hints into this exception.

mercurial/error.py

@@ -18,7 +18,7 b' class HintException(Exception):'
         Exception.__init__(self, *args)
         self.hint = kw.get('hint')
 
-class RevlogError(Exception):
+class RevlogError(HintException):
     pass
 
 class FilteredIndexError(IndexError):