Add a test for type combinations allowed for compound assignment

There are bugs where browsers and/or drivers allow compound assignments
to an lvalue of a scalar type with an rvalue of a vector/matrix type,
even though they should not. Add a test that covers this plus other
combinations for compound assignment. It is not an error when the lvalue
has a vector/matrix type and the rvalue has a scalar type.

This is the first test for the 1.0.4 test suite, so also update test
suite version number to 1.0.4 in code and documentation.
I'll fix this.