p10: acknowledge incoming KICKs with a PART
p10: acknowledge incoming KICKs with a PART

Per https://github.com/evilnet/nefarious2/blob/ed12d64/doc/p10.txt#L611-L616. This fixes autorejoin-on-kick not working with prefix modes because the remote verifies whether the KICK has been acknowledged properly. Closes #465.

GLolol/PyLink