The Depends decorator allows you to optionally remove functions if sepecific globals/modules don't exist. This is particuarly helpful in larger scale deployments where some functions of the module work everywhere, but others require (for example) a service to be installed. This way you can avoid having to try/except all over the module to only load certain functions etc.
Some packages, carbon and graphite-web for example, install their packages to a specific root, using a `virtualenv` or not. `pip freeze` won't show those packages as installed.
* `salt.states.pip.installed()` now keeps a reference to the output of the `__salt__['pip.install']()` call. The reason for this is that we need to know and pass along any information about an eventual error when running that call. This is now done in addition to the old behaviour.
* Add some tests which triggered the issue.
* `salt.modules.file.contains()`, `salt.modules.file.contains_regex()`, `salt.modules.file.contains_glob()` and `salt.utils.find` now do the searching/matching against chunks of data; using defaults, 32KB chunks of data in files; instead of searching/matching line by line.
* Based on the above changes `salt.states.file.append()`, when checking if the text to append is already present, now uses `salt.modules.file.contains_regex()` in order to match spanning multiple lines ignoring the addition/deletion of white-space or new lines, except inside commas.
* The regex used on the above item is built at runtime using `salt.utils.build_whitepace_splited_regex()`, just feed the text to it and you'll get back the proper regex to the matching/searching on, for example `salt.modules.file.contains_regex()`.
* Added tests for all this code.
