handle undef
o export BtceFee
o truncate rate or 'You incorrectly entered one of fields.' is the error message; wish this was documented
o bail in _apiprice if args are not specified or _apiget returns undef
o set nonce to 1/2 INT_MAX as suggested on freenode/#btc-e; one bit less entropy for avoiding the random need to get a new api key (presuming this is the case if nonce reaches INT_MAX)
o set a max retry of 30 in _post