Add in history_usernum and history_username indices. This allows for
searches on *who* made changes to run faster. The best example of this
is on the homepage when it looks for the last modified customers by the
current user. On our system that query could take 5 minutes across so
many history records. Now takes a manageable amount of time with this
index
Merge branch 'h_cust_main_index_fix' of https://github.com/Jayceh/Freeside