match: add narrowmatcher class
This class can be used to adapt an existing match object to a new
match object that only cares about paths within a certain
subdirectory.
% setup repository
adding .hgeol
adding a.txt
% hg clone repo repo-2
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
% printrepr.py a.txt
first\r
second\r
third\r
% hg cat a.txt
first
second
third
% hg clone repo repo-3
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
% printrepr.py a.txt
first
second
third
% hg clone -r 1 repo repo-4
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 2 changes to 2 files
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
% cat .hgeol
[patterns]
**.txt = native
% printrepr.py a.txt
first\r
second\r
third\r