[autotest] tst_QPrinter::taskQTBUG4497_reusePrinterOnDifferentFiles unstable

The test is under qtbase\tests\auto\printsupport\kernel\qprinter

On windows 7 64b, 32b build, the test is unstable.

On linux, fedora 17, the test is always failing.

On windows the error is:

FAIL! : tst_QPrinter::taskQTBUG4497_reusePrinterOnDifferentFiles() Compared values are not the same
Actual (file1.readAll()): 25 21 50 53 2D 41 64 6F 62 65 2D 33 2E 30 0D 0A 25 25 54 69 74 6C 65 3A 20 64 6F 63 75 6D 65 6E 74 31 0D 0A 25 25 43 72 65 61 74 6F 72 3A 20 50 53 63 ...
Expected (file2.readAll()): 25 21 50 53 2D 41 64 6F 62 65 2D 33 2E 30 0D 0A 25 25 54 69 74 6C 65 3A 20 64 6F 63 75 6D 65 6E 74 31 0D 0A 25 25 43 72 65 61 74 6F 72 3A 20 50 53 63 ...
tst_qprinter.cpp(997) : failure location