WIP: Backwards compatibility for Cartesian macros (ngenerate & nsplat)

[timholy]

Just queuing this up, but the changes to master have to happen first.

[simonster]

This doesn't seem to work for functions that use both @ngenerate and Cartesian macros, e.g.:

julia> @ngenerate N Nothing function f(X::NTuple{N,Any}...)
       @ncall N println X
       end;

julia> f((1, 2))
ERROR: UndefVarError: X_1 not defined
 in anonymous at none:2

[simonster]

I thought maybe just calling macroexpand from inside the stagedfunction might work, but that gives me an undefined symbol error. It seems like the macro expansion takes place in whatever module is being interpreted and not the module that calls macroexpand.

[simonster]

#42 seems to fix this.

[timholy]

Thanks, @simonster.