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.

I've put it back both in the test (sent separately) and in Matrices and Data Frames. Thanks for keeping my honest here. I'm not multitasking very well.

I should check out for a few hours, but would like to get this nailed down first. I'm testing the two modified lessons now (I pushed them a few minutes ago.)