grab-bag of cleanups and fixes
- bugfixes:
* added missing argument to Env() constructor
* added missing loop counter update when binding function locals
* checkArguments was misusing array.some(), expecting the specific truthy result (some() just returns true, grr...)
* MemberExpression case matches .object and .property fields, not .left and .right
- added a couple missing checks where it was supposed to be recursively type-checking subexpressions
- cleaned up tests, added a couple more tests
function calls require fixed call syntax as per the 2013/10/11 draft
generated stack trace includes source location info