Improved support for libhdfs

There is a few problems with current libhdfs support

* with hadoop 2.5.1, it should be linked to libhhdfs.a, not liblibhdfs.a
* it was linked directly with the libjvm.so, but the path should be added to the runtime path
* it was linked to fio, but not gfio
* makefile don't use environnement variables any more