Bug: //a[@b='../../@b'], Condition expression with parent query(../../) expression filter

[zhengchun]

This bug from #73.

s := `<?xml version="1.0" encoding="UTF-8"?>
	<?xml-stylesheet type="text/xsl" href="MeasDataCollection.xsl"?>
	<measCollecFile xmlns="http://www.3gpp.org/ftp/specs/archive/32_series/32.435#measCollec">
		<measData>
			<managedElement localDn="foobar.example.com" />
			<measInfo measInfoId="metric_name">
				<measType p="1">field1</measType>
				<measType p="2">field2</measType>
				<measValue measObjLdn="identifier">
					<r p="1">31854</r>
					<r p="2">159773</r>
				</measValue>
			</measInfo>
			<measInfo measInfoId="metric_name2">
				<measType p="1">field3</measType>
				<measType p="2">field4</measType>
				<measValue measObjLdn="identifier">
					<r p="1">1234</r>
					<r p="2">567</r>
				</measValue>
			</measInfo>
		</measData>
	</measCollecFile>`

doc, _ := xmlquery.Parse(strings.NewReader(s))
list := xmlquery.Find(doc, "//r[@p=../../measType/@p]")
for _, n := range list {
    fmt.Println(n.OutputXML(true))
}

Expected(4 nodes):

<r p="1">31854</r>
<r p="2">159773</r>
<r p="1">1234</r>
<r p="2">567</r>

But actually:

<r p="1">31854</r>
<r p="1">1234</r>

only got 2 nodes, missing 159773 and 567