Allow file.append() to use multiple files with templating.
( hopefully closes http://github.com/saltstack/salt/issues/6905 )

This change allows you to use constructs like the following in .sls
files (/tmp/foo will have the concatination of all three files added
to it) :

/tmp/foo:
  file:
      - append
      - template: jinja
      - sources:
          - salt://foo/part1.tmpl
          - salt://foo/part2.tmpl
          - salt://foo/part3.tmpl
      - defaults:
          custom_var: "default value"
          other_var: '123'
	  override_me: 'fail!'

{% if grains['os'] == 'Debian' %}
      - context:
          custom_varx: "override"
          override_me: 'Pass!'
{% endif %}
Merge branch 'develop' of https://github.com/mech422/salt into develop