allow $x ~~ s/// to return Match or list of Match

s/// is now implemented in terms of .subst-mutate, which returns
the matches instead of the result, just as normal matching does.
Back out adding Metamodel::Primitives on Parrot.

It breaks the build, for a likely hard-to-debug reason.
default to uname if it exists

The previous code assumed all Unix distributions could eventually be
enumerated somehow, which is delusional.  :)
Remove non-builtins from deftrap

It clutters up deftrap, and a new Perl 6 user might attempt something
like 'stat', and when they get the error message and they try '.stat'
and don't get the result they expect, it could be very confusing.
Bump NQP_REVISION for latest MoarVM.

Includes fixes for a qqx related crash that often showed up on OSX.
things that go bump in the nqp
Merge branch 'nom' into newio