Ensure absolute path is used for library

[`System#load`][1] requires an absolute path.  If the extraction
directory (`library.${name}.path` or `java.io.tmpdir`) is relative, the
extraction will succeed, but the `System#load` call will fail, resulting
in the library not being loaded.  This commit rectifies that by
obtaining the absolute path to the directory before extracting.

[1]: http://docs.oracle.com/javase/7/docs/api/java/lang/System.html#load(java.lang.String)
Merge pull request #16 from NJAldwin/use-absolute-path

Ensure absolute path is used for library extraction and loading