Replaced some inline values swapping by an explit 'swap' method for making the code easier to read.
This helps also in Matrix.inverse() implementation. We rely on Hotspot optimization for producing
the same performance than when the swapping was done inline.


git-svn-id: https://svn.apache.org/repos/asf/sis/branches/JDK7@1522970 13f79535-47bb-0310-9956-ffa450edef68