diff: pass the diff matcher to the copy logic This passes the existing diff matcher instance down to the copy logic so copy tracing can be more efficient when possible and only trace copies for matching files. This only actually affects forwardcopies (i.e. Given A<-B<-C<-D, it works for 'hg diff -r B -r D foo.txt', but not for 'hg diff -r D -r B foo.txt') since backward copies require walking all histories, and not just the individual file's. This reduces 'hg diff -r A -r B foo.txt' time from 15s to 1s when A and B have 80,000 files different.

copies: add matcher parameter to copy logic This allows passing a matcher down the pathcopies() stack to _forwardcopies(). This will let us add logic in a later patch to avoid tracing copies when not necessary (like when doing hg diff -r 1 -r 2 foo.txt).

treemanifest: extract parse method from constructor When we start to lazily load submanifests, it will be useful to be able to create an treemanifest instance before manifest data gets parsed into it. To prepare for this, extract the parsing code from treemanifest's constructor to a separate method.