util.datamanager: shorten store_exists() and cleanup code.
mod_muc_log_http: refactor code slightly,
- Reduce table indexing by localizing table functions
- Don't access the string table to call match() call it through the metamethod
mod_muc_log_http, util.datamanager: update headers and bump up versioning.
mod_storage_sql: last code cleanup passage.
mod_muc_log_http: change name of a missed call to store_exist.
mod_muc_log_http: code layout rectification.