IDL: annotations on type references change the referenced type

The IDL compiler allows annotations on type references, and applies them on the referenced type.

As can be seen in the test output file simple.avpr, the type MD5 has the property "foo"="bar".

But in the input file simple.avdl:

• The type definition in lines 39-40 has no such property
• Line 53 adds the property to the type for the field hash,
• But it's also silently added to the type for the field nullableHash in line 55

Solution: do not accept annotations for type references.