Update branch alias to 0.7
Merge branch 'master' into develop
Merge branch 'master' into develop
Merge branch 'master' into develop
Merge branch 'master' into develop
Improve exceptions in Gd driver's open()

- RuntimeException more suitable (and consistent with other drivers)
- Change message as file existence is checked beforehand in checkPath() (refs #326)
Add test for opening of an invalid image file
Merge branch 'gd-open' of github.com:vlakoff/Imagine into vlakoff-gd-open
Merge branch 'vlakoff-gd-open'
Update changelog