Revision 570108

Added an equals(String) method to the XMLString interface.  This allows the
caller to compare an XMLString to a Java String without forcing the XMLString
to be converted to a String.

In this particular class (XString), modified equals(XMLString) to take advantage
of the new XMLString.equals(String).  If the argument for the comparison
contains a java.lang.String, then comparing that with the String held by this
XString is likely the fastest way to perform the comparison; otherwise, we give
the argument the chance to compare itself natively with the String contained by
this XString.

Part of patch for XALANJ-1243.  Reviewed by Brian Minchau (minchau@ca.ibm.com).