Rearrange t/ for reuse with multiple Perl 6 implementations.

[cmarcelo]

Rearrange t/ so that it is suited for reuse with multiple Perl 6 implementations. The generic Perl 6 tests, suitable to all Perl 6 implementations, go in t/, and if any tests seem to be implementation specific, then perhaps this indicates the standard needs updating.

[cmarcelo]

Also from TASKS file:

Re-group the majority general/implementation-generic Perl 6 tests first along lines of what is likely to be implemented together and/or by tier, a trivial example already in place being the sanity tests. With the sanity tests plus Test.pm being tier zero, each additional tier can incorporate progressively more "difficult" features, and not assume that anything in tiers above it will work, only that those in tiers below it do. This progression can be similar to how various other technical standards (such as XML or SQL) can come in tiers, with minimum mandatory plus optional