First, handle cases where we have %s in a tt_want or tt_assert.
Second, add tt_want_*_op that do a tt_*_op test, but do not exit the
test on failure.
We should push these upstream to tinytest some time.
The big win here is that we can get process-level isolation.
This has been tested to work okay on at least Linux and Win32. Only
the tests in regress.c have been converted wrapped in the new wrapper
functions; the others are still on the old system.
svn:r1073
