memctx: calculate exact status being committed from specified files Before this patch, "memctx._status" is initialized by "(files, [], [], [], [], [], [])" and this causes "memctx.modified" to include not only modified files but also added and removed ones incorrectly. This patch adds "_status" method to calculate exact status being committed according to "files" specified at construction time. Exact "_status" is useful to share/reuse logic of committablectx. This patch is also preparation for issues fixed by subsequent patches. Some details of changes for tests in this patch: - some filename lines are omitted in "test-convert-svn-encoding.t", because they are correctly listed up as "removed" files those lines are written out in "localrepository.commitctx" for "modified" and "added" files by "ui.note". - "| fixbundle" filterring in "test-histedit-fold.t" is omitted to check lines including "added" correctly "fixbundle" discards all lines including "added".