Processes a file name to make sure it is valid and has the correct suffix and extension File names with an extension (e.g. ".XPT") are not altered

Processes a file name to make sure it is valid and has the correct suffix and extension File names with an extension (e.g. ".XPT") are not altered

process_file_name(file_name, year, extension = ".XPT")

Arguments

file_name	name of the file
year	NHANES cycle year
extension	file extension