tests: new test for mq qdiff command
`hg qdiff .' is supposed to work but it is currently broken.
This test should help us verify when it gets fixed.
%% no changes
%% no changes
%% uncompressed contents in repo
this is a test
%% uncompress our working dir copy
this is a test
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
%% uncompress our new working dir copy
this is a test