Update mach from gecko tree

python/mach/docs/driver.rst

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+.. _mach_driver:
+
+=======
+Drivers
+=======
+
+Entry Points
+============
+
+It is possible to use setuptools' entry points to load commands
+directly from python packages. A mach entry point is a function which
+returns a list of files or directories containing mach command
+providers. e.g.:
+
+.. code-block:: python
+
+   def list_providers():
+       providers = []
+       here = os.path.abspath(os.path.dirname(__file__))
+       for p in os.listdir(here):
+           if p.endswith('.py'):
+               providers.append(os.path.join(here, p))
+       return providers
+
+See http://pythonhosted.org/setuptools/setuptools.html#dynamic-discovery-of-services-and-plugins
+for more information on creating an entry point. To search for entry
+point plugins, you can call
+:py:meth:`mach.main.Mach.load_commands_from_entry_point`. e.g.:
+
+.. code-block:: python
+
+   mach.load_commands_from_entry_point("mach.external.providers")
+
+Adding Global Arguments
+=======================
+
+Arguments to mach commands are usually command-specific. However,
+mach ships with a handful of global arguments that apply to all
+commands.
+
+It is possible to extend the list of global arguments. In your
+*mach driver*, simply call
+:py:meth:`mach.main.Mach.add_global_argument`. e.g.:
+
+.. code-block:: python
+
+   mach = mach.main.Mach(os.getcwd())
+
+   # Will allow --example to be specified on every mach command.
+   mach.add_global_argument('--example', action='store_true',
+       help='Demonstrate an example global argument.')