Fix bug in equals() that made caching effect-less.

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/trunk@557934 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/fop/fo/properties/FixedLength.java

      * {@inheritDoc}
      */
     public boolean equals(Object obj) {
-        if (obj instanceof EnumProperty) {
+        if (obj instanceof FixedLength) {
             return (((FixedLength)obj).millipoints == this.millipoints);
         } else {
             return false;