Handle MPMN parts with no arguments correctly
Tell typechecker about String.encode method
Add set difference - op to mgcollections
Handle outside operators with unknown definitons

Previously, the compiler would crash when an operator defined in another
module was used, because it expected to be able to see the parameter
types fully.
Allow references to defs in their initialisation
Remove obsolete tests
Apply small bugfixes revealed by IDR
Add first pass at identifier resolution phase
Make IDR phase default instead of typechecker
Permit unqualified self-calls to inherited methods
Remove typechecker
Fix GCT generation with new IDR pass
Handle cross-module imports again
Fix tarballs now typechecker gone
Fix JS now typechecker gone
Restore support for "is parent" hack
Remove verbose output from undefined identifiers
Re-enable plugin infrastructure with new API
Allow qualified type names in block params
Remove deprecated "length" pseudo-method