Start trying to use callstatic where possible.
Avoid double-walking trees in sink context.

Before, we'd walk the tree under the non-void and void branches of
the QAST::Want. This prevents the double-work, cutting a good bit
off the optimize phase.
On JVM, eliminate binder for zero-param code.

This in turn means it'll be elligible for the indy optimization that
relates to such calls.
Don't pass nqp::null to a QAST node!
Make paramless block opt on JVM a level 3.

Breaks some spectests. Need better analysis before it can become a
level 2. Doesn't break anything in the setting itself, though, so we
can keep the benefit from better optimizing that.
Merge branch 'opts' into nom