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.