Reproducible builds

Reproducible builds

At the moment ngircd fails the tests for reproducible builds in Debian
since it uses the __DATE__ and __TIME__ macros for the INFO command.

Instead of patching this out I decided to implement an optional
constant BIRTHTIME that allows you to set a time stamp for the "Birth
Date" information, in seconds since the epoch, like in

    export CFLAGS += -DBIRTHTIME=$(shell date +%s --date="2015/08/15 23:42:22")

In the future, Debian will provide a SOURCE_DATE_EPOCH environment
variable, dealing with the situation until then will be my job.

The time format was taken from the NGIRCd_StartStr formatting in
ngircd.c so the "Birth Date" and "On-line since" lines in the INFO
output look similar:

    :irc.example.net 371 nick :ngIRCd 22.1-IDENT+IPv6+IRCPLUS+PAM+SSL+SYSLOG+ZLIB-x86_64/pc/linux-gnu
    :irc.example.net 371 nick :Birth Date: Tue Aug 25 2015 at 18:11:11 (CEST)
    :irc.example.net 371 nick :On-line since Tue Aug 25 2015 at 18:11:33 (CEST)
    :irc.example.net 374 nick :End of INFO list

The format of the time stamped is changed, but as far as I can tell, there's no
rule that is violated by that.

Bonus level: Reformat the messages so the time stamps are aligned.