Improve colonpair-extended names on subroutines
Improve colonpair-extended names on subroutines

Per discussion: https://irclog.perlgeek.de/perl6/2017-01-25#i_13988088

- sub foo:bar<ber> {} no longer throws and is a valid extended sub name
    - this also fixes inconsistency where this form threw *except* in cases
        when sub was some_exiting_token_in_Perl6_Grammar:sym<some_exiting> {}
- sub foo:<ber> {} throws X::Syntax::Extension::Category, as before
- sub foo:bar<ber>:sym<meow> now throws X::Syntax::Reserved, as we want
    :sym<> to be reserved. HOWEVER, a 6.c-errata test[^1] expects foo:sym<>
    to throw X::Syntax::Extension::Category instead, so I left this form to
    throw that old exception. The Proper Way™ for all :sym<> versions is
    left commented out with a TODO next to it, to be used in 6.d language

[1] https://github.com/perl6/roast/blob/dfe905a8ce84d09b5b0536fcc151e798488a9289/S32-exceptions/misc.t#L132

usev6/rakudo,softmoth/rakudo,rakudo/rakudo,lucasbuchala/rakudo,salortiz/rakudo,awwaiid/rakudo,salortiz/rakudo,salortiz/rakudo,tbrowder/rakudo,raydiak/rakudo,raydiak/rakudo,Gnouc/rakudo,tony-o/rakudo,labster/rakudo,nbrown/rakudo,softmoth/rakudo,tbrowder/rakudo,nbrown/rakudo,MasterDuke17/rakudo,nbrown/rakudo,jonathanstowe/rakudo,tbrowder/rakudo,awwaiid/rakudo,lucasbuchala/rakudo,usev6/rakudo,tony-o/rakudo,Gnouc/rakudo,tony-o/rakudo,jonathanstowe/rakudo,rakudo/rakudo,tony-o/rakudo,lucasbuchala/rakudo,samcv/rakudo,raydiak/rakudo,Gnouc/rakudo,sjn/rakudo,labster/rakudo,tony-o/rakudo,usev6/rakudo,MasterDuke17/rakudo,Gnouc/rakudo,labster/rakudo,rakudo/rakudo,nbrown/rakudo,sjn/rakudo,rakudo/rakudo,samcv/rakudo,tbrowder/rakudo,rakudo/rakudo,awwaiid/rakudo,Gnouc/rakudo,labster/rakudo,jonathanstowe/rakudo,softmoth/rakudo,awwaiid/rakudo,lucasbuchala/rakudo,nbrown/rakudo,rakudo/rakudo,salortiz/rakudo,sjn/rakudo,MasterDuke17/rakudo,nbrown/rakudo,lucasbuchala/rakudo,MasterDuke17/rakudo,jonathanstowe/rakudo,usev6/rakudo,Gnouc/rakudo,tony-o/rakudo,labster/rakudo,softmoth/rakudo,salortiz/rakudo,softmoth/rakudo,tbrowder/rakudo,samcv/rakudo,usev6/rakudo,labster/rakudo,sjn/rakudo,awwaiid/rakudo,samcv/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,samcv/rakudo,raydiak/rakudo,sjn/rakudo,tbrowder/rakudo,jonathanstowe/rakudo,salortiz/rakudo