Import byacc-20121003.

This is a significant update for yacc that's being maintained by Thomas
Dickey at http://invisible-island.net/byacc/.
Merge branch 'vendor/BYACC'
Update build for byacc import.
Fix warnings from byacc import.
atc game: lex cleanup
m4: define yylex based on __DragonFly_version

The old lex wants it and emits errors if it's not there.
The new lex doesn't want it, and emits warnings if it is there.
On gcc44, the build breaks on an error.
To make both happy, switch it on based on recent __DragonFly_version bump.

Bump __DragonFly_version to be 100% everyone can upgrade
Fix buildkernel for lex/yacc upgrades, too.
Merge branch 'master' into gsocdrm_merger