dredge: reworked checking for allowed term combination (marginality checks)
 it is now based on term dependency matrices returned by getAllTerms
new function 'nested.within'
updateable: new argument 'eval.args'

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/mumin@296 edb9625f-4e0d-4859-8d74-9fd3b1da38cb