Use sys.prefix instead of a fixed, possibly broken path with resources

[Marco Giusti]

Actually the resources are searched in a limited, fixed set of paths: "/usr/share/pixmaps/" and "/usr/local/share/pixmaps/". As per distutils documentation, the data_files is interpreted as following:

Each (directory, files) pair in the sequence specifies the installation directory and the files to install there. If directory is a relative path, it is interpreted relative to the installation prefix (Python’s sys.prefix for pure-Python packages, sys.exec_prefix for packages that contain extension modules). Each file name in files is interpreted relative to the setup.py script at the top of the package source distribution.

so using sys.prefix should be enough.