hghave: allow adding customized features at runtime Before this patch, there is no way to add customized features to `hghave` without changing `hghave` and `hghave.py` themselves. This decreases reusability of `run-tests.py` framework for third party tools, because they may want to examine custom features at runtime (e.g. existence of some external tools). To allow adding customized features at runtime, this patch makes `hghave` import `hghaveaddon` module, only when `hghaveaddon.py` file can be found in directories below: - `TESTDIR` for invocation via `run-tests.py` - `.` for invocation via command line The path to the directory where `hghaveaddon.py` should be placed is added to `sys.path` only while importing `hghaveaddon`, because: - `.` may not be added to `PYTHONPATH` - adding additional path to `sys.path` may change behavior of subsequent `import` for other features `hghave` is terminated with exit code '2' at failure of `import hghaveaddon`, because exit code '2' terminates `run-tests.py` immediately. This is a one of preparations for issue4677.

import-checker.py: exit with code 0 if no error is detected Before this patch, `import-checker.py` exits with non-0 code, if no error is detected. This is unusual as Unix command. This change may be a one of preparations for issue4677, because this can avoid extra explanation about unusual exit code of `import-checker.py` for third party tool developers.

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.

templatekw: allow the caller of showlist() to specify the join() separator The keyword {latesttag} currently manually joins the list of tags using ':', which prevents a transparent switch over to a hybrid list.