first attempts at more testing and comparison with SuperC
improve corner cases of lexer

- #ifdef +3
update infrastructure
correct terminology: parse -> lex
extract common interface for partial preprocessors: VALexer
start wrapping XtcPreprocessor and testing typechef tests with it
fix sat solver caching
some debug code and failing test
alternative seq method, closer to paper
changed parameter order
fixed joinOptList operator and some code cleanup
enforce stronger invariants: no dead elements in the tree
fix tests
eliminate type warnings
deactivate pgp plugin, unnecessary for now
attempt to use new scala version
deactivate pgp plugin, unnecessary for now
fix compiler error (erasure)
add forgotten test files
no error when .fm file is not found