the \ifxetex boolean for testing whether the TeX-variant
XeTeX is being used for typesetting.
Also provides the \RequireXeTeX command which throws
an error if XeTeX is not the engine in use.
WWW: http://www.ctan.org/tex-archive/macros/generic/ifxetex/
PR: ports/127607
Submitted by: Martin Dieringer <martin.dieringer@gmx.de>
