XQilla version 2.2.4 released

This is a bug fix release for XQilla 2.2, including the ability to compile against Xerces-C 3.1.0, and a small number of miscellaneous fixes.

Change Log:
* Modified to build against Xerces-C 3.1.0
* Modified the DOM 3 API to only orphan grammars if PSVI is enabled.
* Fixed computed attribute constructors not to use the default element
namespace for names.
* Modified node serialization to generate prefixes for attributes with
no prefix but in a namespace.
* Modified node serialization to use existing prefixes if possible.
* Fixed an unknown exception during certain update operations.
* Build fix for Sun Workshop 6 compiler.
* Build fix for older GCC.
* Added maintainer mode (--enable-maintainer-mode) to rebuild build
related files.