Invocation: renamed dontBoxSequence to isSpread
Invocation #908: added isArgumentSpread(int argIndex) method

to be able to know if a given argument is spread, as opposed to the last one being spread
ExpressionTransformer #908: implement partial variadic spread for positional invocations

non-Java invocations
Test for #908: partial variadic spread for positional non-Java invocations
Test for #908: added partial spread comprehensions
Test for #908: Test Callable and partial variadic spread
AbstractTransformer #908: support partial spread in java method spread conversion
ExpressionTransformer #908: don't convert expr type iff this param is spread
ExpressionTransformer #908: Implement partial variadic spread for java methods
Test for #908: Implement partial variadic spread for Java methods
Updated .src to match with current language module
model loader tests: don't compare two lazy models
Fixed RangeOpIterationOptimization test due to better flow analysis in the type checker