hgweb: use revsymbol() to determine if query is a revision

repo.__getitem__ is about to get dumber.

Differential Revision: https://phab.mercurial-scm.org/D3155

mercurial/hgweb/webcommands.py

@@ -248,7 +248,7 b' def _search(web):'
 
     def getsearchmode(query):
         try:
-            ctx = web.repo[query]
+            ctx = scmutil.revsymbol(web.repo, query)
         except (error.RepoError, error.LookupError):
             # query is not an exact revision pointer, need to
             # decide if it's a revset expression or keywords