added sample masking to pivotal engine as an option

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/abernethy@92 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
completion of abremPivotals

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/abernethy@93 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
changed getPPP first output column title to time (changed from data)
added reserved argument interval to getPPP and alias.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/abernethy@94 edb9625f-4e0d-4859-8d74-9fd3b1da38cb