Use getCanonicalPath instead of getAbsolutePath for native library tests

Was running into some issues with these tests and switching it to getCacnonicalPath fixed it. Absolute path was returning "..." for some reason, not sure why. Test result looked like:

    [junit] Testcase: testMatchUnversionedToVersioned(com.sun.jna.NativeLibraryTest):	FAILED
    [junit] Latest versioned library not found when unversioned requested expected:<.../...> but was:<......>
    [junit] junit.framework.ComparisonFailure: Latest versioned library not found when unversioned requested expected:<.../...> but was:<......>
    [junit] 	at com.sun.jna.NativeLibraryTest.testMatchUnversionedToVersioned(NativeLibraryTest.java:192)
    [junit] 
    [junit] 
    [junit] Testcase: testAvoidFalseMatch(com.sun.jna.NativeLibraryTest):	FAILED
    [junit] Library with similar prefix should be ignored expected:<.../...> but was:<......>
    [junit] junit.framework.ComparisonFailure: Library with similar prefix should be ignored expected:<.../...> but was:<......>
    [junit] 	at com.sun.jna.NativeLibraryTest.testAvoidFalseMatch(NativeLibraryTest.java:207)

See:

http://meatwad.mouf.net/rubick/poudriere/logs/bulk/10amd64-default/2014-02-26_18h52m31s/logs/errors/jna-4.0_1.log

for more details.