[10dc6daa37] [gets] on a non-blocking channel must take care so that
    1) At least one call to the channel driver input proc gets made.
       Failure to do this locks up the channel - catastrophic FAIL. 
    2) After any driver call reports BLOCKED, don't call again.
       This is less serious, but FAILs to respect the non-blocking setting.
Code corrections and tests included, to restore 8.5.15 compat.