Sugar should refuse to run as root user

[mchua]

Running Sugar as the root user can disable access to Sugar for all non-root users. This appears to be the result of files crucial to running Sugar being created/modified with permissions inaccessible to non-root users. See  https://bugzilla.redhat.com/show_bug.cgi?id=547805#c3 for reference.

Sugar should check to see if the user is root before starting; if the user is root, Sugar should refuse to run, and instead print an explanatory error message as to why this is the case and how the user can run sugar as a non-root user.