Remove 'has' for primitive fields.  Dynamic version always returns true.  This also means that primitives are always included in text format, even if they are default-valued.

Require a colon before 'group' or 'union' except for unnamed unions as well as the legacy case of a named union with an ordinal (where the colon is optional).

Fix compiler bugs.  Now test.capnp compiles to an identical schema to the old Haskell compiler, minus intentional changes.