tests/test-hghave.t

hgweb: don't call sys.exit() in httpservice.run()

If I'm reading the code correctly, `mercurial.server.createservice()`
can return an hgweb service or one of three types of command server
services. The caller then calls `mercurial.server.runservice()`,
passing it the returned service's run method. Only the hgweb service
was calling `sys.exit()`. It has been that way since 8d44649df03b
(refactor ssh server., 2006-06-04). That commit message doesn't
provide any explanation. Let's clean up and have the code follow the
usual return path into the `dispatch` module.

After this patch, there should be no remaining places left where we
call `sys.exit()` except for valid uses in the `dispatch` and `worker`
modules.

Differential Revision: https://phab.mercurial-scm.org/D9272

  $ . "$TESTDIR/helpers-testrepo.sh"

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
  $ ( \
  > testrepohgenv; \
  > "$PYTHON" $TESTDIR/run-tests.py --with-hg=`which hg` -j 1 \
  >    $HGTEST_RUN_TESTS_PURE test-hghaveaddon.t \
  > )
  running 1 tests using 1 parallel processes 
  .
  # Ran 1 tests, 0 skipped, 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 <<NO_CHECK_EOF
  > importing this file should cause syntax error
  > NO_CHECK_EOF

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