Fixed argument check of EnvironmentVariableOperation.

Task-number: QTIFW-286

Change-Id: I4c8cb25f70a05c7a5a3754e46680767d4b345523
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>
Reviewed-by: Karsten Heimrich <karsten.heimrich@digia.com>
Use standard form of error strings in AppendFileOperation.

Change-Id: I49a3e987b509cf833d92c732aa48b81ae260eb45
Reviewed-by: Karsten Heimrich <karsten.heimrich@digia.com>