console: Default interact version to JavaScript 1.8
console: Default interact version to JavaScript 1.8

We were inconsistent in our default version handling; for scripts
and command line arguments we used the #define from context.c,
but for simply "gjs" we used "default", i.e. 1.5.

This is broken since many overrides like dbus.js haven't been
down-ported to 1.5.

pixunil/cjs,magcius/gjs,magcius/gjs,magcius/gjs,djdeath/gjs,endlessm/gjs,pixunil/cjs,mtwebster/cjs,djdeath/gjs,mtwebster/cjs,mtwebster/cjs,endlessm/gjs,endlessm/gjs,mtwebster/cjs,magcius/gjs,endlessm/gjs,pixunil/cjs,djdeath/gjs,djdeath/gjs,magcius/gjs,djdeath/gjs,endlessm/gjs,mtwebster/cjs,pixunil/cjs,pixunil/cjs