test-extension: fix disabled extension tests for run-tests.py --local
One test that requires inserting a broken extension into hgext does this
by modifying PYTHONPATH. This doesn't work when run with --local because
the 'hg' script being used is in the same directory as the local hgext.
Instead of modifying PYTHONPATH, a secondary extension is enabled using
--config that inserts the dummy hgext at the beginning of sys.path,
before the script's path.
% test default params, display nothing because of delay
% test with delay=0, refresh=0
loop [ ] 0/3
loop [=====================> ] 1/3
loop [============================================> ] 2/3
% test refresh is taken in account
% test format options 1
0/2 loop lo
1/2 loop lo
% test format options 2
0/2 p.0 [ ]
1/2 p.1 [=================================> ]
% test format options and indeterminate progress
0 loop.0 [ <=> ]
1 loop.1 [ <=> ]
% test immediate progress completion