The implementation is a bit circumvoluted, but we do need to share
options between the top-level and js/src configures, possibly with
different defaults, and to properly pass things down from one to
the other. Until we are further down the road and can actually merge
both configures, this is a necessary evil.
Because --enable-application is the current way to do things, transpose
it to configure.py, but since --enable-application=js doesn't make
sense, make it an alias of a new --enable-project option.
This only partially moves --enable-application out of old-configure.in
because there are a lot of other things intertwined with it.
