added params to behave like dir()

2013-06-13: added full.names & trailing slash.
2013-06-19: added pattern argument, for consistency with dir()
bug fix ncol's were equal

2013-08-28: added explicit check for same colnames if ncol's are equal.
bug fix: prevent vector being returned

2013-09-03: bug fix where a 2 column table became a vector
made collate an S3 generic

converted collate.data.frame into S3, by adding collate.default method
new testcases
auto-updated by roxygen2
auto-update due to changes to collate method