DON'T MERGE: Fix for expr creates var failure in R Programming

The original test, expr_creates_var, fails when AUTO_DETECT_NEWVAR is TRUE and the user creates extraneous variables, e.g. misspelling a name, in the course of answering a question. A custom test of the same name masks the original and ignores extraneous values. The custom test is included in Vectors and in Matrices and Data Frames.

The original test is also used in Regression Models, but since I believe AUTO_DETECT_NEWVAR is FALSE in all or most of its lessons, I've not altered them yet. I'm checking for problems
@WilCrofter Did you mean to remove the `calculates_same_value()` custom test here? I replaced `creates_val_identical_to()` with it like you suggested.