Add option for gtk3.
Rename "gtk" option to gtk2.
Change default from gtk to gtk3.

Correct a comment while here.

Bump PKGREVISION.
Updated editors/emacs24 to 24.3nb5
Use MAKE_DIRS to create installation directory for default config file.
Bump PKGREVISION.
Updated devel/at-spi2-core to 2.8.0nb1