Don't assume that the current system is a derivate of Debian.

Builds on non-debian systems failed automatically because apt-get is unavailable.
Added an explicit check for two package managers, which will still try to automatically install.
Otherwise, assume the dependencies are installed and continue the process.
The script can still fail later on anyway.
Merge pull request #79 from kevinvandervlist/dev

Don't assume that the current system is a derivative of Debian.