zmodem_recv_files() now returns upon first failed file.

Previously, a ZRINIT frame would be sent even after a failed file download, and this could be misinterpreted by the sender as a successful file receipt 
 acknowledgement. 'lrz' just completely aborts the receive "batch" under the same conditions, so we'll just do the same to prevent the sender (e.g. BBS) from mistakenly counting this as a successful transfer (download).

A lot of log message updates: additions, removals, and use of the __FUNCTION__ macro.