vegan: CRAN release v2.3-4

Main reason for this release was that texi2dvi (an external system software) version 6.1 introduced incompatible features that prevented building vegan (issue #158). This release removes texi2dvi dependence in a vignette. All other vignettes are also built and can be accessed with standard R tools. Other changes: linestack failed in some cases when the labels argument was used. index 19 had a typo on betadiver. vegandocs was deprecated: we use now standard R tools