util: appdata_file_call and appdata_file_find_first functions
Use appdata_file_call to find BFGMiner config file(s)
Accept --default-config option to search and load default configuration files, even if user is specifying their own
Add failover_only pool flag, to avoid using it regardless of strategy

Ignored by failover and loadbalance strategies (use priority and quota for those)
Automatically add pool configured from bitcoin.conf for failover only
Merge branch 'auto_solomine' into bfgminer