Custom install prefix

[Jesper Pedersen]

In order to get a custom install prefix to work I had to change

https://github.com/plasma-umass/coz/blob/master/coz#L51

to

coz_runtime = coz_prefix + path_sep + '..' + path_sep + 'lib' + path_sep + 'libcoz.so'

[Charlie Curtsinger]

Thanks for the fix. This should be working now.