prevent aliases being defined recursively to fix #524
Conflicts:
	src/com/redhat/ceylon/compiler/typechecker/model/ProducedType.java
Merge branch 'master' of https://github.com/ceylon/ceylon-spec
fix #530 by relaxing type constraint checking on types that appear in
is conditions (we can relax more syntactic positions later) 
Conflicts:
	src/com/redhat/ceylon/compiler/typechecker/analyzer/ExpressionVisitor.java
quickly fix the test
support for native annotation #348
Merge branch 'master' of https://github.com/ceylon/ceylon-spec into 533

Conflicts:
	src/com/redhat/ceylon/compiler/typechecker/analyzer/ExpressionVisitor.java
	test/main/aliases/Aliases.ceylon
	test/main/aliases/unionintersection.ceylon