Fix problems with \middle. #1023

[dpvc]

Surround \middle with OPEN and CLOSE TeXAtoms, so that the spacing will be consistent with TeX's version (e.g., \mathrel{}\middle|\mathrel{} will produce the right spacing). As a side effect, this resolves the problem with the quotes, sot this resolves issue #1023.

[zorkow]

lgtm.

Question: What happens on a TEX.ERROR? Will that lead to a math processing error?

[dpvc]

What happens on a TEX.Error?

The TeX input processor will stop parsing the expression and produce an merror element that includes the error message. If the noErrors extension is in play, then the error causes the original TeX code to be displayed rather than the error message (this was requested by AMS long ago, though personally I think it is a mistake to have it in the combined config files).

Will that lead to a math processing error?

No. Those should only come from errors in the MathJax javascript code, not from errors in the user input (which should be reported like the one at line 1340 here).

[pkra]

though personally I think it is a mistake to have it in the combined config files).

+1