Check a neededFile for commonly needed auxiliary files

Currently, this is only used for shapefiles.

.checkForAuxiliaryFiles(neededFiles)

Arguments

neededFiles	A character string of file name(s) that will be checked. Specifically if the file extension is .shp it will output the names of files with these extensions also: c("shx", "dbf", "prj", "sbx", "sbn") files also.