decouple CDeclUse from the type system to make it optional
better error messages
merge split parse results after parsing into single AST

previously, typechef only performed type checking
if the parser succeeded in all configurations.
this was overly strict. now it proceeds with all
successful results in the corresponding contexts
Merge branch 'master' of git://github.com/ckaestne/TypeChef

Conflicts:
	CTypeChecker/src/main/scala/de/fosd/typechef/typesystem/CDeclTyping.scala
	CTypeChecker/src/main/scala/de/fosd/typechef/typesystem/CExprTyping.scala
	CTypeChecker/src/main/scala/de/fosd/typechef/typesystem/CTypeEnv.scala
	Frontend/src/main/scala/de/fosd/typechef/Frontend.scala