[PERDITION-USERS] IPv6 address literals in --bind_address (1.19_rc4)

Each server in the --bind_address option list passes through the function user_server_port_strn_assign() (in perdition/server_port.c) which separates the user, server and port components. This function does not recognize IPv6 address literals as documented in RFC 3986 (i.e., IPv6 addresses enclosed in brackets.) For example, address literal [2001:db8:1000:1::2] will be separated into "server" [2001:db8:1000:1: and "port" 2] , which are syntactically incorrect and will produce an error in getaddrinfo(). The enclosed patch adds IPv6 literal handling. (A workaround is to use a "naked" IPv6 address with the port specification, e.g., 2001:db8:1000:1::2:110 , but this is a) ugly and b) not standards-compliant.) i.