Now using the '==' and '!=' operators instead of instanceof and getClass().
Changed the typechecker so it doesn't throw exceptions but appends errors to an error list.
Modified tests so they also use the error list instead of exceptions.
Merge branch 'JessevanAssen-master'

Conflicts:
	JessevanAssen/src/org/uva/sea/ql/typechecker/TypecheckerVisitor.java
Merge branch 'master' of https://github.com/software-engineering-amsterdam/sea-of-ql