[PATCH] o.a.f.fo.properties.CondLengthProperty.equals() uses object identity

Due to the usage of object identity to compare two objects for equality, the org.apache.fop.fo.properties.PropertyCache is not working effectively. This applies to instances of CondLengthProperty and CommonBorderPaddingBackground instances that use it.

The test case was provided by Ron Vandenbranden, see
http://markmail.org/message/vvr2k4cii3273fos

Before applying the patch, transforming the attached FO to PDF logs the messages:
INFO: 10 hashCode() collisions for org.apache.fop.fo.properties.CondLengthProperty
Jun 14, 2012 1:12:27 AM org.apache.fop.fo.properties.PropertyCache fetch
INFO: 10 hashCode() collisions for org.apache.fop.fo.properties.CommonBorderPaddingBackground

After applying the patch, there should be no log messages related to hashCode() collisions.