tests/readers/tex/*.native:  removed EXTRA newlines

introduced by last change.
TeXMath writer:  only give space after \quad, \quadd.

The other space commands should not have spaces after.
TeXMath writer:  put braces around EGrouped, except at top level.

This is needed for e.g.

    \sin {x+2}
Don't put braces around single-token identifers.
TeXMath writer: Removed extra spaces after binary.
TeXMath writer:  remove brace before close } unless it's escaped.
TeXMath writer: Add space after operators.