isfilelist: Checks whether datadir is a directory or a vector with
filenames
Description
Checks whether argument datadir used in various other functions in
GGIR is the name of a directory that includes data files or whether
it is a vector with the full paths to one or more data files
Usage
isfilelist(datadir)
Value
Boolean whether it is a list of files (TRUE) or not (FALSE)
Arguments
datadir
Argument datadir as used in various other functions in GGIR