Monitor disk-space on file-systems used for building
We store intermediate build data in the g_get_user_cache_dir() along with other things like code-search indexes. Therefore, we should monitor the file-system containing this so that the user can be notified if it is running out of disk space.
We should probably warn the user (using an info bar or equivalent) if there is less than 1 GB.
The user can react to the warning in one of to ways. Simply acquiesce the notification, or run a clean-up operation. The clean-up operation could use a DzlDirectoryReaper to remove old data in the cache directory that is past a certain age. We probably want to start with projects that are not open (and wipe them out completely), followed by any non-active builds for the current project.