Make it possible to disable projects

There are two reasons we should be able to have disabled projects:

- You were following a project before, but would like to stop watching new updates to it (eg. with l10n_drupalorg, it should not continue looking for new releases and downloading certain modules you stop translating)
- The automated system might pick up modules from drupal.org which you might or might not want to actually carry on the server. Before you decide to enable them, they should be disabled.

This patch is an enabler of sorts. It does not do automated discovery of (by default) disabled modules or provide a user interface to disable projects just yet. The underlying infrastructure is built however, and the parsing / discovery code takes care of leaving disabled projects alone.

This patch also includes a new l10n_drupalorg.admin.inc, and fix for message handling (reported in http://drupal.org/node/212637) and non-existent file handling in l10n_localpacks (which helps people starting up an l10n_server to debug).