Added OpenSuse 13.1 and 13.2 support in preinstall.sh script.
Added OpenSlide support in preinstall script.
Added unit tests for Deep Zoom and OpenSlide.
This was needed on my docker container running Debian Jessie. This is the error without it:
```text
Package libgsf-1 was not found in the pkg-config search path.
Perhaps you should add the directory containing `libgsf-1.pc'
to the PKG_CONFIG_PATH environment variable
Package 'libgsf-1', required by 'vips', not found
gyp: Call to 'PKG_CONFIG_PATH=":$PKG_CONFIG_PATH:/usr/local/lib/pkgconfig:/usr/lib/pkgconfig" pkg-config --libs vips' returned exit status 1. while trying to load binding.gyp
```
