run-tests: teach Test instances whether they are in unittest mode
Tests executing in unittest mode behave a little differently. For
example, they report their results to a TestResult rather than just
printing. This patch paves the way for better integration of Test into
the unittest framework.
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls
a
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
B should disappear
$ ls
a