QSF backend, support for partial QofBooks, merge fix, references and KVP

[Neil Williams]

Log Message:
-----------
QSF backend, support for partial QofBooks, merge fix, references and KVP support

Tags:
----
gnucash-gnome2-dev

Modified Files:
--------------
    gnucash:
        ChangeLog
    gnucash/src/app-file:
        gnc-file.c
    gnucash/src/backend/qsf:
        pilot-qsf-GnuCashInvoice.xml
        qsf-backend.c
        qsf-map.xsd.xml
        qsf-object.xsd.xml
        qsf-xml-map.c
        qsf-xml.c
        qsf-xml.h
    gnucash/src/engine:
        gnc-date.c
        kvp_frame.c
        kvp_frame.h
        qof_book_merge.c
        qofbackend-p.h
        qofbackend.h
        qofsession.c
        qofsession.h