Also combine the login page's JS.

Change-Id: I705f692f8cdb3c953a28196149bd576017d391e2
Add tests for the up_to_date function & fixes.

Test the various cases that might occur, and switch to using the
files' mtime, rather than ctime, as this is the more useful value.

Change-Id: Iaba1c4264e616c8b8128dbf5d6c3a5ad54dbf9ec
Make and ignore the web cache folder.

This is the folder that stores the combined CSS & JS files.

Change-Id: I5e97fc78b7de70e4765d587b62d0ca4fffbb009a