Fix RT #123176
copy STD's better undef message
Eat the terminator before changing languages

Note this doesn't eat any whitespace, so generally something like:

    rule statementlist { '' … }

will be wanted to eat the leading whitespace after the use statement, if
the language is whitespace-insignificant.
Merge branch 'nom' of http://github.com/rakudo/rakudo into nom
Update pre-Lolly comment
fix .subbuf when overlapping the end
Add twigil ~ to the grammar
implement IO::Handle.input-line-separator
Initial stab at getting $~Vars to work
Add parse to Slang.pm

Still too many issues with NQP/Perl 6 interactions, but it at least
makes $~vars a little easier to play with
a p6bool "basically" boxes an int.

may want to invent a second flag "BOXED_NORMALIZED" or
so that would only allow boxing/unboxing skipping if the
result is used in an if/unless op.
Merge branch 'nom' into newio