When a tunnel parameter is created in an xsl:with-param
element in a call of xsl:call-template, a static error
is produced saying that the parameter isn't declared in
the called template.
Also, if call-template calls a template that contains
<xsl:param name="p" required="yes"" tunnel="yes">, a
static error is produced saying that no value is
supplied for the required parameter.
Source code fixed.
Tests added: var 25-27.