Inheritance of classes with a qualifier parameter

If a class extends a @HasQualifierParameter class (or implements a
@HasQualifierParameter interface), then that class must also be marked
@HasQualifierParameter. A particular subclass should be able to specify which qualifier
parameter should be used for the super class. (This is similar to class StringList implements List<String> {...}.) For example,

 @HasQualifierParameter(Tainted.class)
 class Buffer {
     void append(@PolyTainted Buffer this, @PolyTainted String s) { ... }
 }
 @HasQualifierParameter(Tainted.class)
 @Tainted class TaintedBuffer extends @Tainted Buffer {
     @Override
     void append(@Tainted TaintedBuffer this, @Tainted String s) { ... } // legal override
 }

@Untainted TaintedBuffer is an invalid type.

See test case in checker/tests/tainting/SubClassHasQP.java and manual section in generics.tex.

Start with checker/tests/tainting/SubClassHasQP.java and the related manual section in generics.tex. Read the existing test and documentation to understand the expected inheritance and qualifier-parameter rules. Done means subclasses of @HasQualifierParameter classes or interfaces must declare the annotation, valid qualifier selection works for the superclass, and invalid types such as @Untainted TaintedBuffer are rejected.