Please describe the problem:
libxslt fails to compile a stylesheet that contains a template whose pattern references a variable

Steps to reproduce:
xsltproc test.xsl test.xml

Here's test.xsl:
  <?xml version="1.0"?>
  <stylesheet version="1.0" xmlns="http://www.w3.org/1999/XSL/Transform">
    <output method="xml" encoding="UTF-8"/>
    <variable name="var" select="'val'"/>
    <template match="element[@attr=$var]">OK</template>
  </stylesheet>

The input test.xml is simply:
  <?xml version="1.0" encoding="UTF-8"?>
  <element attr="val"/>

Actual results:
XPath error : Undefined variable
compilation error: file test.xsl line 5 element template
Failed to compile predicate

Expected results:
Should output "OK".

According to the XSLT 1.0 Spec, variable references are allowed within a pattern:
  Pattern -> RelativePathPattern -> StepPattern -> Predicate ->
    PredicateExpr -> Expr -> OrExpr -> AndExpr -> EqualityExpr ->
    RelationalExpr -> AdditiveExpr -> MultiplicativeExpr ->
    UnaryExpr -> UnionExpr -> PathExpr -> FilterExpr ->
    PrimaryExpr -> VariableReference

Does this happen every time?
Yes

Other information:
xsltproc --version says:
  Using libxml 20627, libxslt 10120 and libexslt 813
  xsltproc was compiled against libxml 20627, libxslt 10119 and libexslt 813
  libxslt 10120 was compiled against libxml 20627
  libexslt 813 was compiled against libxml 20627

This test case worked on libxslt 1.1.12, so the regression was introduced sometime between 1.1.12 and 1.1.19.  I suspect that it was broken by Changeset 1330:
  http://svn.gnome.org/viewcvs/libxslt?view=revision&revision=1330