run-tests.py: add TESTDIR to PATH if it differs from RUNTESTDIR Before this patch, `RUNTESTDIR` is added to `PATH`, but `TESTDIR` isn't. This doesn't cause any problems, if `run-tests.py` runs in `tests` directory of Mercurial source tree. In this case, `RUNTESTDIR` should be equal to `TESTDIR`. On the other hand, if `run-tests.py` runs in `tests` of third party tools, commands in that directory should be executed with explicit `$TESTDIR/` prefix in `*.t` test scripts. This isn't suitable for the policy "drop explicit $TESTDIR from executables" of Mercurial itself (see 4d2b9b304ad0). BTW, 4d2b9b304ad0 describes that "$TESTDIR is added to the path" even though `TESTDIR` isn't added to `PATH` exactly speaking, because `TESTDIR` and `RUNTESTDIR` weren't yet distinguished from each other at that time. This is a one of preparations for issue4677.

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.

run-tests.py: execute hghave by the path relative to run-tests.py Before this patch, `run-tests.py` executes `hghave` by the path relative to `TESTDIR` (= cwd of `run-tests.py` running). This prevents third party tools for Mercurial from running `run-tests.py`, which is placed in `tests` of Mercurial source tree, in `tests` of own source tree. In such cases, `TESTDIR` refers the latter `tests`, and `hghave` doesn't exist in it. This is a one of preparations for issue4677.

templatekw: make {latesttag} a hybrid list This maintains the previous behavior of expanding {latesttag} to a string containing all of the tags, joined by ':'. But now it also allows list type operations. I'm unsure if the plural handling is correct (i.e. it seems like it is usually "{foos % '{foo}'}"), but I guess we are stuck with this because the singular form previously existed.