arithmetic operations now push 'Invalid Type' on stack if operands are not of the same type
added integration tests for dividision
Merge branch 'master' of github.com:SWP-Ubau-SoSe2014-Haskell/SWPSoSe14
changed the output assertion a little bit #40
error handling for div by zero, invalid types and stack underflow #38 #40 #42 #45 #46
Merge branch 'master' of github.com:SWP-Ubau-SoSe2014-Haskell/SWPSoSe14