Makefile adapded for pbuilder

Hi Erik,

I'm building the package for ubuntu, and I encountered the following error. When you build a package, you cannot use absolute paths in the make install, because if you do that, you'll get a permission error and the package could not be built. This is due to security reasons. 

The debian/ubuntu packaging system uses a chroot to install the package, so to make it works I had to apply this patch. Here this is explained in a more detailed way: http://wiki.debian.org/HowToPackageForDebian (ctrl+F DESTDIR).

The patch doesn't affect the "make install" in it's normal way. If you do a "make install" in a local installation, the software will install as always. But with this patch you can also specify the DESTDIR (which is what the debian/ubuntu building system does).

Would you mind to include it in your source please?

Thank you very much!