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.
% create source repository
adding a
adding b
% clone and pull to break links
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
created new head
% relink
relinking .hg/store
collected 5 candidate storage files
not linkable: 00changelog.i
not linkable: 00manifest.i
not linkable: data/b.i
pruned down to 2 probably relinkable files
relink: data/a.i 1/2 files (50.00%)
not linkable: data/dummy.i
relinked 1 files (136 bytes reclaimed)
% check hardlinks
repo/.hg/store/data/a.i == clone/.hg/store/data/a.i
repo/.hg/store/data/b.i != clone/.hg/store/data/b.i