Rebuild the composer.json file and run composer update only when necessary while enabling a module via Drush

Attached patch seems to work. Couple of things to point out...

• The logic is changed to leverage Composer Manager's hook_enable() implementation for the composer.json rebuild. This eliminates the file being built twice.
• I also implemented Drush's disable hook so that dependencies are removed when a module containing a composer.json file is disabled

We should also explore adding an option in the UI to neither rebuild the composer.json file nor prompt the user to update Composer dependencies. The use case here is if you have a site in production where you don't want to ever modify composer.json and the packages it manages but have to disable a module in an emergency. On hosted platforms you might not have the ability to write to these locations anyways depending on how it is set up and how the application is configured.

Same functionality, modified comments in composer_manager_write_if_changed() for clarity.

Marking as needs work to implement the setting mentioned in #1.

Attached patch adds the setting.

I'm super-psyched about this patch because I think it really improves the DX and allows people to not have to think about Composer when installing and disabling modules via Drush, so I am committing.

http://drupalcode.org/project/composer_manager.git/commit/1a51e83