[PATCH] run-tests: fix -i when testcases are used

[Jun Wu]

Excerpts from Martin von Zweigbergk's message of 2017-06-20 21:48:05 -0700:
> On Tue, Jun 20, 2017 at 9:45 PM, Jun Wu <quark at fb.com> wrote:
> > # HG changeset patch
> > # User Jun Wu <quark at fb.com>
> > # Date 1498019662 25200
> > #      Tue Jun 20 21:34:22 2017 -0700
> > # Node ID 30a98655ab27976c2020e20909093e2cb678758b
> > # Parent  0ce2cbebd74964ffe61e79de8941461bccc9371b
> > # Available At https://bitbucket.org/quark-zju/hg-draft 
> > #              hg pull https://bitbucket.org/quark-zju/hg-draft  -r 30a98655ab27
> > run-tests: fix -i when testcases are used
> 
> What was broken?

./run-tests.py -i with a .t test using "#testcases".

The fix was just one line - to detect ".t" correctly. Otherwise the .t test
will be treated like a ".py" and "-i" won't update ".t" file.