Copy grain matcher to create pillar matcher.

[tvaughan]

First, please see the pillars documentation:
http://salt.readthedocs.org/en/latest/topics/pillar/index.html. Next,
perhaps an example will explain this best...

Let's say you have a /src/pillar/top.sls that looks like:

base:
  'hostname1':
    - production
  'hostname2':
    - development

And a /srv/pillar/production.sls that looks like:

role: production
countrycode: us

And a /srv/pillar/development.sls that looks like:

role: development
countrycode: cl

This means that /srv/salt/top.sls could now look like:

base:
  '*':
    - ssh
  'role:production':
    - match: pillar
    - users.production
    - default
    - clojure
  'role:development':
    - match: pillar
    - users.development
    - default.dev
    - clojure.dev

Both role and countrycode may also be used as a template variable
as explained in the pillar documentation above.

For a real-world example, please see:

• https://github.com/rentalita/ubuntu-setup
• https://github.com/rentalita/ubuntu-setup/blob/master/salt/apt/init.sls.
• https://github.com/rentalita/ubuntu-setup/blob/master/salt/apt/sources.list

This commit also extends the salt command-line client so that it too
may use the pillar matcher, like:

salt -I 'role:production' test.ping

Documentation and tests are not included in this commit. These will
come in a later commit.

The pillar_match routine is simply a copy of the grain_match
routine. But I grep'd for the exsel matcher to figure out what parts
of the code needed to be touched in order to (hopefully) make this
work. I suppose a pillar pcre matcher could be made just as easily.

[thatch45]

This looks great Tom! It is in, keep up the awesomeness!

[tvaughan]

Ha! I'm flattered. The pleasure is mine.

[thatch45]

Matchers are a core part of the Salt system, and having more in here helps a great deal. That and you have been on fire!

[tvaughan]

Sorry that I didn't provide the docs and tests like I said I would. Looks like @thatch45 added these in later commits. Is there anything left that needs to be added that I could do?