tests/test-hghave.t

util: adjust hgcmd() to handle frozen Mercurial on OS X

Previously, 'hg serve -d' was trying to exec the bundled python executable,
which failed with:

    Unknown option: --
    usage: python [option] ...
    Try 'python -h'...
    abort: child process failed to start

See the previous patch for details about the content of the various command
variables.  Note that unlike the previous patch here an application bundling
Mercurial could set $HG in the environment to get the correct result, there
isn't anything that a bundling application could do to get the correct result
here.

'hg serve -d' now launches under TortoiseHg, and there is a process listed in
the background, but a client process cannot connect to it for some reason, so
more investigation is needed.

Testing that hghave does not crash when checking features

  $ hghave --test-features 2>/dev/null

Testing hghave extensibility for third party tools

  $ cat > hghaveaddon.py <<EOF
  > import hghave
  > @hghave.check("custom", "custom hghave feature")
  > def has_custom():
  >     return True
  > EOF

(invocation via run-tests.py)

  $ cat > test-hghaveaddon.t <<EOF
  > #require custom
  >   $ echo foo
  >   foo
  > EOF
  $ run-tests.py $HGTEST_RUN_TESTS_PURE test-hghaveaddon.t
  .
  # Ran 1 tests, 0 skipped, 0 warned, 0 failed.

(invocation via command line)

  $ unset TESTDIR
  $ hghave custom

(terminate with exit code 2 at failure of importing hghaveaddon.py)

  $ rm hghaveaddon.*
  $ cat > hghaveaddon.py <<EOF
  > importing this file should cause syntax error
  > EOF

  $ hghave custom
  failed to import hghaveaddon.py from '.': invalid syntax (hghaveaddon.py, line 1)
  [2]