8066943: (fs) Path.relativize() gives incorrect result for ".."

[Alan Bateman]

The relativize method has been problematic for sometime when used with 
paths containing "." or "..". Normalizing the paths first will make it 
work for most cases but there are corner cases that are still not right. 
The following patch updates the implementations to do the right thing.

    http://cr.openjdk.java.net/~alanb/8066943/webrev/

The bulk of the changes are new tests to make sure that all the cases 
are covered.

-Alan