updated release notes to include behavior changes in multiple regression

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/branches/MATH_2_X@1073663 13f79535-47bb-0310-9956-ffa450edef68

RELEASE-NOTES.txt

@@ -14,6 +14,12 @@ This release contains some minor compatibility breaks with version 2.1 in some i
  the arguments of the EventState.reinitializeBegin method have changed;
  some protected fields which already had public accessors in AbstractStepInterpolator have been replaced.
 
+There is a behavior change that users of the multiple regression classes should be aware of. In version
+2.1, there was no way to estimate models without intercept terms, and, while this was not clear from
+the documentation, design (X) matrices needed to include initial unitary columns.  In 2.2, initial 
+unitary columns are not necessary and whether or not models include intercept terms is configurable.
+See the change log and javadoc for the classes in org.apache.commons.math.stat.regression for details.
+
 The major new features are:
  a new FastMath class, both faster, more accurate and with a few additional functions than StrictMath and Math;
  a new package for floating point arbitrary precision computing, including high level functions like exponential, sine, square root ...;