compare grep result between target and its parent
I found that typical case is that grep target is added at (*) revision
in the tree shown below.
+--- 1(*) --- 3
0
+--- 2 ------ 4
Now, I expect 'hg grep --all' to show only rev:1 which is first
appearance of target line.
But 'hg grep --all' will tell:
target line dis-appeared at 3 => 4
target line appeared at 2 => 3
target line dis-appeared at 1 => 2
target line appeared at 0 => 1
because current 'hg grep' implementation compares not between target
revision and its parent, but between neighbor revisions in walkthrough
order.
I checked performance of this patch by "hg grep --follow --all
walkchangerevs" on whole Mercurial repo, and patched version could
complete as fast as un-patched one.
