Neil Williams' QSF Backend.

[Derek Atkins]

Log Message:
-----------
	Neil Williams' QSF Backend.

	* configure.in: add checks for libxml2 (requires >= 2.5.10)
	* src/backend/qsf: new backend directory
	* src/app-file/gnc-file.c: add new QSF error strings
	* src/backend/file/gnc-backend-file.[ch]: detect for QSF input files
	* src/engine/qofbackend.[ch]: know how to load the QSF backend

Tags:
----
gnucash-gnome2-dev

Modified Files:
--------------
    gnucash:
        ChangeLog
        configure.in
    gnucash/src/app-file:
        gnc-file.c
    gnucash/src/backend:
        Makefile.am
    gnucash/src/backend/file:
        Makefile.am
        gnc-backend-file.c
        gnc-backend-file.h
    gnucash/src/backend/file/test:
        Makefile.am
    gnucash/src/engine:
        qofbackend.h
        qofsession.c

Added Files:
-----------
    gnucash/src/backend/qsf:
        Makefile.am
        pilot-qsf-GnuCashInvoice.xml
        qsf-backend.c
        qsf-dir.h.in
        qsf-map.xsd.xml
        qsf-object.xsd.xml
        qsf-xml-map.c
        qsf-xml.c
        qsf-xml.h