Cache reporter user data in view_all_bug_page

Add the reporter id to the array of users to be cached from the bug
filter result. This saves later individual sql queries from
user_cache_row()

Changed the temporary arrays to be associative indexed by id, so we
don't need to call 'array_unqiue' later.

Fixes 0020258

Signed-off-by: Damien Regad dregad@mantisbt.org