Include libxml headers during compile (#121026).

[Derek Atkins]

Log Message:
-----------
Include libxml headers during compile (#121026).

	* src/backend/file/Makefile.am:
	* src/backend/file/test/Makefile.am:
	* src/business/business-core/file/Makefile.am:
	  Need to include GNOME_XML_CFLAGS to make sure the libxml includes
	  are found during the compile.  Fixes #121026.

Tags:
----
gnucash-1-8-branch

Modified Files:
--------------
    gnucash:
        ChangeLog
    gnucash/src/backend/file:
        Makefile.am
    gnucash/src/backend/file/test:
        Makefile.am
    gnucash/src/business/business-core/file:
        Makefile.am