Fixes QImage constructor signature that used string buffer as image data source.

The fixes uses the patch provided by Pieter Palmers on the bug #489
description[1].

A very simple test, to check the signature existence, was added.

[1] http://bugs.openbossa.org/show_bug.cgi?id=489

Reviewed by Hugo Parente <hugo.lima@openbossa.org>
Reviewed by Luciano Wolf <luciano.wolf@openbossa.org>

tests/QtGui/qimage_test.py

@@ -0,0 +1,20 @@
+
+'''Test cases for QImage'''
+
+import unittest
+
+from PySide.QtGui import QImage
+
+from helper import UsesQApplication
+
+class QImageTest(UsesQApplication):
+    '''Test case for calling setPixel with float as argument'''
+
+    def testQImageStringBuffer(self):
+        '''Test if the QImage signatures receiving string buffers exist.'''
+        img0 = QImage('', 100, 100, QImage.Format_ARGB32)
+        img1 = QImage('', 100, 100, 0, QImage.Format_ARGB32)
+
+if __name__ == '__main__':
+    unittest.main()
+