get test-query to fail consistently.

[Derek Atkins]

Log Message:
-----------
get test-query to fail consistently.

PERR() when xaccTransGetSharePrice() overflows.
Loop test-query, and start the rng to fail consistently.

Modified Files:
--------------
    gnucash/src/engine:
        Transaction.c
    gnucash/src/engine/test:
        test-query.c