tests/test-known.t

run-tests.py: add RUNTESTDIR to refer `tests` of Mercurial

Before this patch, there is no way to refer files under `tests` or so
of Mercurial source tree, when `run-tests.py` runs in `tests` of third
party tools. In this case, `TESTDIR` refers the latter `tests`.

This prevents third party tools from using useful tools in Mercurial
source tree (e.g. `contrib/check-code.py`).

This patch adds `RUNTESTDIR` environment variable to refer `tests` of
Mercurial source tree, in which `run-tests.py` now running is
placed. For example, tests of third party tools can refer
`contrib/check-code.py` in Mercurial source tree as
`$RUNTESTDIR/../contrib/check-code.py`.

BTW, for similarity with `TESTDIR` referring `test*s*` directory,
newly added environment variable isn't named as `RUNTEST*S*DIR`. In
addition to it, the corresponded local variable is also named as
`runtestdir`.

This is a one of preparations for issue4677.

#require killdaemons

= Test the known() protocol function =

Create a test repository:

  $ hg init repo
  $ cd repo
  $ touch a ; hg add a ; hg ci -ma
  $ touch b ; hg add b ; hg ci -mb
  $ touch c ; hg add c ; hg ci -mc
  $ hg log --template '{node}\n'
  991a3460af53952d10ec8a295d3d2cc2e5fa9690
  0e067c57feba1a5694ca4844f05588bb1bf82342
  3903775176ed42b1458a6281db4a0ccf4d9f287a
  $ cd ..

Test locally:

  $ hg debugknown repo 991a3460af53952d10ec8a295d3d2cc2e5fa9690 0e067c57feba1a5694ca4844f05588bb1bf82342 3903775176ed42b1458a6281db4a0ccf4d9f287a
  111
  $ hg debugknown repo 000a3460af53952d10ec8a295d3d2cc2e5fa9690 0e067c57feba1a5694ca4844f05588bb1bf82342 0003775176ed42b1458a6281db4a0ccf4d9f287a
  010
  $ hg debugknown repo
  

Test via HTTP:

  $ hg serve -R repo -p $HGPORT -d --pid-file=hg.pid -E error.log -A access.log
  $ cat hg.pid >> $DAEMON_PIDS
  $ hg debugknown http://localhost:$HGPORT/ 991a3460af53952d10ec8a295d3d2cc2e5fa9690 0e067c57feba1a5694ca4844f05588bb1bf82342 3903775176ed42b1458a6281db4a0ccf4d9f287a
  111
  $ hg debugknown http://localhost:$HGPORT/ 000a3460af53952d10ec8a295d3d2cc2e5fa9690 0e067c57feba1a5694ca4844f05588bb1bf82342 0003775176ed42b1458a6281db4a0ccf4d9f287a
  010
  $ hg debugknown http://localhost:$HGPORT/
  
  $ cat error.log
  $ killdaemons.py