ClaytonOakes: no visible global function definition for 'tail'
biprobit.time: no visible global function definition for 'tail'
biprobit.time.trunc.test: no visible global function definition for
  'tail'
compare.twinlm: no visible global function definition for 'getS3method'
corsim.prostate: no visible global function definition for 'plot'
corsim.prostate: no visible global function definition for 'lines'
easy.binomial.twostage: no visible global function definition for
  'head'
easy.twostage: no visible global function definition for 'head'
eventpois: no visible global function definition for 'glob2rx'
eventpois: no visible global function definition for 'dsort'
phreg.par: no visible global function definition for 'tail'
piecewise.data: no visible global function definition for 'head'
piecewise.twostage: no visible global function definition for 'head'
plot.bptwin: no visible global function definition for 'tail'
plot.bptwin: no visible global function definition for 'plot'
plot.bptwin: no visible global function definition for 'lines'
plot.casewise: no visible global function definition for 'plot'
plot.casewise: no visible global function definition for 'lines'
plot.claytonoakes: no visible global function definition for 'dev.list'
plot.claytonoakes: no visible global function definition for 'lines'
plot.claytonoakes: no visible global function definition for 'plot'
plot.cumh: no visible global function definition for 'plot'
plot.cumh: no visible global function definition for 'polygon'
plot.cumh: no visible global function definition for 'lines'
plot.eventpois: no visible global function definition for 'plot'
plot.eventpois: no visible global function definition for 'tail'
plot.eventpois: no visible global function definition for 'lines'
plot.phreg: no visible global function definition for 'lines'
plot.phreg: no visible global function definition for 'plot'
plot.timemets: no visible global function definition for 'plot'
plot.timemets: no visible global function definition for 'tail'
plot.timemets: no visible global function definition for 'lines'
plot.twinlm: no visible global function definition for 'par'
plot.twinlm: no visible global function definition for 'plot'
plot.twostage: no visible global function definition for 'plot'
plot.twostage: no visible global function definition for 'title'
plot.twostage: no visible global function definition for 'lines'
plot.twostage: no visible global function definition for 'abline'
plotcr: no visible global function definition for 'par'
plotcr: no visible global function definition for 'dev.interactive'
plotcr: no visible global function definition for 'devAskNewPage'
plotcr: no visible global function definition for 'plot'
plotcr: no visible global function definition for 'points'
summary.twinlm: no visible global function definition for
  'capture.output'
surv.boxarea: no visible global function definition for 'head'
Undefined global functions or variables:
  abline capture.output dev.interactive dev.list devAskNewPage dsort
  getS3method glob2rx head lines par plot points polygon tail title
Consider adding
  importFrom("grDevices", "dev.interactive", "dev.list", "devAskNewPage")
  importFrom("graphics", "abline", "lines", "par", "plot", "points",
             "polygon", "title")
  importFrom("utils", "capture.output", "getS3method", "glob2rx", "head",
             "tail")
to your NAMESPACE file.