* 'pvalueinterval' gained a 'z' argument (not for end-users)

* 'midpvalue' uses 'pvalueinterval' with 'z = 0.5'

* 'pvalueinterval' returns a named result


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/coin@915 edb9625f-4e0d-4859-8d74-9fd3b1da38cb