match: make _fileroots a @propertycache and rename it to _fileset The files in the set are not necesserily roots of anything. Making it a @propertycache will help towards extracting a base class for matchers.

fsmonitor: use modern match API It seems like fsmonitor/__init__.py was based on a pretty old version of dirstate.py. Let's copy over the changes from the following two commits: 55c449345b10 (match: add isexact() method to hide internals, 2014-10-29) 3c346969c321 (dirstate: avoid match.files() in walk(), 2015-05-19)

diffstat: properly count lines starting in '--' or '++' (issue5479) Lines that start in '--' or '++' were previously not counted as deletions or additions in diffstat, resulting in incorrect addition/deletion counts. The bug was present if the start of the line, combined with the diff character resulted in '---' or '+++'. diffstatdata will now track, for each file, if it has moved pas the header section by looking for a line beginning with '@@'. Once that has happened, lines beginning with '-' or '+' will be counted for deletions and additions. Once a line beginning with 'diff' is found, the process starts over.

test-http-bad-server: match different in output Same as for previous update, the longer port number can affect this ouput.

config: make config.items() return a copy config.items() was iterating over a copy of the data for the the specified section on Python 2 by using .items(). However, on Python 3, items() does not make a copy, so let's switch to explicitly making a copy to make it safe on both Python 2 and Python 3.

filemerge: store error messages in module variables Copytracing may be disabled because it's too slow (see experimental.disablecopytrace config option). In that case user may get errors like 'local changed FILE which other deleted'. It would be nice to give user a hint to rerun command with `--config experimental.disablecopytrace=False`. To make it possible let's extract error message to variables so that extension may overwrite them.