mod_muc_log_http: use stores pattern search to find available dates
storagemanager: add store_exists function
mod_storage_internal: add store_exists function
mod_storage_sql: add store_exists function
datamanager: add store_exists function
mod_muc_log_http: use store_exists function from datamanager
mod_muc_log_http: day_callback uses store_exists
Merge pull request #97 from jprjr/storage-enhancements

mod_muc_log_http: use datamanager:stores() w/ 'pattern' parameter, use datamanger.store_exists()
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.
util.datamanager: remove debug statement.
mod_muc_log_http: do not path encode the room node as it's already done.