log: remove caching of all visited revisions (issue3253)

Not only does this eat all available memory for some users, it's slower.

mercurial/cmdutil.py

@@ -979,7 +979,7 b' def walkchangerevs(repo, match, opts, pr'
     wanted = set()
     slowpath = match.anypats() or (match.files() and opts.get('removed'))
     fncache = {}
-    change = util.cachefunc(repo.changectx)
+    change = repo.changectx
 
     # First step is to fill wanted, the set of revisions that we want to yield.
     # When it does not induce extra cost, we also fill fncache for revisions in