pop3: satisfy some strict parsing rules in RFC 1939 "Commands in the POP3 consist of a case-insensitive keyword, possibly  followed by one or more arguments.  All commands are terminated by a  CRLF pair.  Keywords and arguments consist of printable ASCII  characters.  Keywords and arguments are each separated by a single  SPACE character."
pop3: satisfy some strict parsing rules in RFC 1939
"Commands in the POP3 consist of a case-insensitive keyword, possibly
 followed by one or more arguments.  All commands are terminated by a
 CRLF pair.  Keywords and arguments consist of printable ASCII
 characters.  Keywords and arguments are each separated by a single
 SPACE character."

"A server MUST respond to an unrecognized, unimplemented, or
 syntactically invalid command by responding with a negative status
 indicator."

Therefore the following commands must be rejected:
LIST 2600Hz
LIST 99 red balloons
TOP 1 2 buckle-my-shoe

Signed-off-by: Phil Carmody <e888d2bd6f13f82caa51a37c03d034c76f661ba3@dovecot.fi>

dscho/dovecot,dscho/dovecot,dscho/dovecot,dscho/dovecot,dscho/dovecot