Phil Longstaff's patch to prevent duplicate pricedb entries.

[Derek Atkins]

Log Message:
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Phil Longstaff's patch to prevent duplicate pricedb entries.

	* src/engine/gnc-pricedb.c:
	  Phil Longstaff's patch to prevent duplicate pricedb entries.

Modified Files:
--------------
    gnucash:
        ChangeLog
    gnucash/src/engine:
        gnc-pricedb.c