add childType argument to ArgSpec.checkTypesAndScope

This is an attempt to fix the weird type-checking errors in the
slam model. Still not sure this is the right fix, as the meaning of
ArgSpec.checkTypesAndScope() is not entirely clear.
remove "@RunWith(JUnit4.class)"

This is not necessary, and for some reason, these tests were excluded
from "sbt test", and could only be run from eclipse.
make TestBuiltInFunctions pass again
Merge branch 'fix-tests' into ppaml-slam
remove one more "RunWith(JUnit4.class)"
TestIsotropicMultivarGaussian.testHighDimensions()