Fix cast to empty interface type. This is a workaround for a
discrepancy between how type names are serialized by the compiler vs
how type expressions are formatted by go/printer.
We allowed integer and pointer type casts everywhere but type casts to
string, []byte and []rune only at toplevel.
Fuse evalToplevelTypeCast and evalTypeCast and allow both kinds
everywhere. There are multiple other ways to create variables than
don't reference user memory anyway (which wasn't the case back when
evalToplevelTypeCast was implemented).
Fixes#1423
Introduces a new TargetGroup abstraction that can be used to manage
multiple related targets.
No actual management of child processes is implemented here, this is
just a refactoring to make it possible to do that in the future.
Updates #2551
When doing a map lookup with a string literal we should load as much of
the keys to at least match the length of the string literal, so that
the lookup doesn't fail with the "string too long" error.
Fixes#3034
Moves variable evaluation tests to pkg/proc which is where most of the
code they test exists, this also allows the removal of a bunch of
duplicate support code.
