(ftp_cat): rewrite error detection/reporting: don't rely on
ferror(), only consult errno in case of error.
This fixes download problems on -current.
Bump version to 0.11nb1.
Changes:
* display transfer rates
* detect stalled connections and abort after stall-timeout seconds
* fix ASCII mode uploads
* write proper URLs (encoding special chars, include user and port)
* various bug fixes