Revert a change -- continue to use GnuCash APIs.

[Derek Atkins]

Log Message:
-----------
Revert a change -- continue to use GnuCash APIs.

	* src/backend/file/sixtp-utils.c:  Revert change.. Make sure
	  we still use gnc_setenv and gnc_unsetenv.

Tags:
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gnucash-gnome2-dev

Modified Files:
--------------
    gnucash:
        ChangeLog
    gnucash/src/backend/file:
        sixtp-utils.c