log speedup: walkchangerevs: filter the files only if we need them
This speeds up hg log and significantly reduces memory usage (max RSS
goes from ~92MB to ~21MB on the kernel repo), since we no longer store
all the revisions in the cache.
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
pulling from ../a
searching for changes
adding changesets
adding manifests
adding file changes
added 2 changesets with 2 changes to 1 files
(run 'hg update' to get a working copy)
merging a and b
0 files updated, 1 files merged, 0 files removed, 0 files unresolved