Support default arguments for the executable

[mkhl]

Some “Run Script” commands supply arguments to the executable that may lead to errors, which caused for example textmate/swift.tmbundle#16.

This change adds a default_args option to #run which is appended to the command line when there is no hashbang line (or parsing them is disabled).

“Run Script” type commands in other bundles will need updating to take advantage of this change.

[mkhl]

The problem mentioned above hit me again while using pytest.

Pytest files are Python scripts that one is supposed to run with pytest, so it would seem sensible to add a hashbang line to that effect:

#!/usr/bin/env pytest

def test_nothing():
    pass

Running the above fails with

usage: pytest [options] [file_or_dir] [file_or_dir] [...]
pytest: error: unrecognized arguments: -u
  inifile: None
  rootdir: /Users/mkhl/Desktop

because Python’s “Run Script” command hardcodes a "-u" argument to the interpreter, which pytest doesn’t understand.
This change together with a change of that command from TextMate::Executor.run(ENV["TM_PYTHON"] || "python", "-u", ENV["TM_FILEPATH"],… to TextMate::Executor.run(ENV["TM_PYTHON"] || "python", ENV["TM_FILEPATH"], :default_args => "-u",… fixes the problem.

The same error occurs when using alternative forms like #!/usr/local/bin/pytest or #!/usr/bin/env python -m pytest.