Make it possible to disable filtering for a pattern.
Rationale: Apparently there were no way to disable for example win32text extension locally.
RFC: Can it already be done another way?
adding bar
adding foo
adding quux1
adding quux2
created new head
merging bar
merging bar failed!
merging foo and baz to baz
1 files updated, 1 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges
U bar
R baz
3 files updated, 0 files merged, 1 files removed, 0 files unresolved
merging bar
merging bar failed!
merging baz and foo to baz
1 files updated, 1 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges
% show unresolved
U bar
R baz
% unmark baz
% show
U bar
U baz
% re-resolve baz
merging baz and foo to baz
% after
U bar
R baz
% resolve all
merging bar
warning: conflicts during merge.
merging bar failed!
% after
U bar
R baz