Support rakudo-jvm builds on smaller systems

Tune JVM memory options to allow successful compile on a
32-bit/2GB RAM system, while still remaining <2% slower to
compile the setting on a larger 64-bit system than the current
settings.

Max heap size was tested every 100m; -Xmx1100m was minimal for
compiles on 32-bit, and -Xmx1300m was minimal on 64-bit, but
noticeably slower than current settings.  -Xmx1600m seemed to
be the sweet spot for minimal slowdown on 64-bit while still
being buildable on a 32-bit/2GB RAM system.

Also explicitly set stack size, as the automatic tuning seemed
to work fine on the larger 64-bit system, but set a too-small
stack on the smaller system, causing the build to fail.
-Xss1m seems to work well on both.
wire NQP's module loader to
udpate NQP_REVISION (module loader changes)
remove blanket instruction for users to implement

<masak> remember, most users have no plans to be core implementors.
<[Coke]> masak, agreed.
properly box sprintfdirective's return value
remove the candidate argument to bless

warn when it is still passed along.
[ROADME] remove an item that has been done

also downgrade typed exceptions, since it is mostly done
[ROADMAP] remove another done item. FROGGS++
Make @a.VAR.name and %h.VAR.name work
Make sure .VAR.name tests are run
Naive implementation of Str.tc and tc(Str)

Waiting for RaNIW to implement nqp::tc as an exercise
Add Any.exists($key) and Any.delete($key)

This feels like a hack, but it seems the best way to handle cases such as

  my %h; say %h<a><b>:exists; say %h<a><b>:!k   # False, "b"

without having to add a large number of candidates for Any:U: in combination
with all possible adverbial pairs and combination of adverbial pairs.
Make sure Bag|Set.delete don't exist (Any.delete vivified them)
Make %h<a><b> := "foo" work; alas, %h<a><b> := my $b doesn't yet
Fix error message fail
It's always in the timing of things: fix "is default(Nil)"
Eradicate .PIR code for range reification

There is no point keeping it around if we have an NQP version around that
also works on Parrot.  And which in the future will be better optimisable.
X::Comp::Trait exception becomes X::Comp::Trait::Unknown
fetch/store to %*ENV directly

... instead of using the thing returned by nqp::getenvhash()
use nqp::shell() instead of pir::spawn

Also bump NQP_REVISION, to pull in pmurias++ patch.