Fix buffer overflow in introduce_client and burst_TS6

If the client being introduced has more than 10 user modes send_umode()
will overflow ubuf
m_version: display charybdis version in /version

Otherwise it just crashes when /version is used.
server: Require EX and IE capabilities (+e and +I cmodes).

The code to send each channel mode only to servers supporting it was
broken a while ago and was not very useful anyway. Therefore, require
all connecting servers to support all standard channel modes.
ircd_parser: Fix inconsistent declaration of yyerror().