mailfs: support for UTF-8 searches

UTF-8 searches with the SEARCH command must
be conducted in two steps: the first sends
the SEARCH command with the length of the
UTF-8 encoded string and the second sends
the literal search term. The searches need
to not be quoted.

R=rsc, david.ducolombier, rsc, 0intro
CC=plan9port.codebot
https://codereview.appspot.com/13244043
1 file changed