added adaptive packages to imports

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/caret@877 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
more NULL declarations to avoid incorrect R CMD check warnings

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/caret@878 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
cleaned up adaptive control parameters

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/caret@879 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
added another helper function to look for missing packages

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/caret@880 edb9625f-4e0d-4859-8d74-9fd3b1da38cb