Tidy up userpoints block titles

In Drupal 5 the user points block title appears in the admin screen as "myusername's points".

The html output is just a plain double encoding bug, but having the users own name appear in the block title is confusing (since it looks like the admin will be adding a block showing only *their* points!).
The attached patch fixes both of these, and removes the build array which is no longer needed. Someone should review the new wording at least!

It also changes the username in the block title (when it is on a page) to t() with a @ placeholder (check_plain() only), rather than the themed t()with % or : placeholders. This is in line with the display used for the username in the core navigation menu block title.