#9 xsl:processing-instruction doesn't work

[Richard Light]

If you have an XSLT stylesheet which uses the
<xsl:processing-instruction> command, it will always
fail because the variable FAllowsTemplateBody is not
set to true.

This means that any subsidiary instructions placed
inside the <xsl:processing-instruction> (in order to
give it some content) will cause a validation error.

The fix for this bug is to override the Create method
for TXpXSLProcessingInstruction, and set
FAllowsTemplateBody to true.