Remove key-ordering sensitivity in fixtures

Previously, the field order was effectively taken from the last record in the fixture, but the values were ordered according to the array_unique call above - primarily determined by the first record in the fixture.  If these two orders differed, values were added under the wrong keys.
Restructuring Strings test so that it is compatible with this change
Merge pull request #1183 from cincodenada/patch-1

Fix bug where differing key-ordering in fixtures causes errors.

When a fixtures first and last records differed data should be
inserted correctly.