run-tests: move diff generation into TestResult
TestResult is the thing that captures all our test results. It's logical
for diff viewing to be handled there and not inside Test.
While writing this patch, it was discovered that Test.fail() was
printing redundant test result output. This has been removed.
Arguments controlling diffs have been removed from Test.__init__.
Issue351: mq: qrefresh can create extra revlog entry
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ hg qinit
$ echo b > b
$ hg ci -A -m foo
adding b
$ echo cc > b
$ hg qnew -f foo.diff
$ echo b > b
$ hg qrefresh
$ hg debugindex b
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 3 ..... 0 1e88685f5dde 000000000000 000000000000 (re)