Please describe the problem:
A libxml2 2.6.23 compiled under solaris 5.9 has some difficulties with a 
pattern which contains "\(.*\)":

[facet 'pattern'] The value '(a)' is not accepted by the pattern '\(.*\)'.

Steps to reproduce:
1. test.xsd:
<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
	<xs:simpleType name="rootType">
		<xs:restriction base="xs:string">
			<xs:pattern value="\(.*\)"/>
		</xs:restriction>		
	</xs:simpleType>

	<xs:element name="root" type="rootType" />
</xs:schema>

2. test.xml:
<?xml version="1.0"?>
<root>(a)</root>
 
3. xmllint --schema test.xsd test.xml 


Actual results:
<?xml version="1.0"?>
<root>(a)</root>
test.xml:2: element root: Schemas validity error : Element 'root': 
[facet 'pattern'] The value '(a)' is not accepted by the pattern '\(.*\)'.
test.xml:2: element root: Schemas validity error : Element 'root': '(a)' is not 
a valid value of the atomic type 'rootType'.
test.xml fails to validate


Expected results:
<?xml version="1.0"?>
<root>(a)</root>
test.xml validates


Does this happen every time?
Yes

Other information: