Revert "Treatment of REException."

This reverts commit 3057ba2027262903ae51247f8aa18d01830efd1e.
Revert "Input preprocessing  – always add XHTML+MathML 1.1 Doctype to allow MathML named entities processing."

This reverts commit 9f3605ed4cbc9e1ad45675b55a89f6356a694f67.