This function converts a string in the
form of "2 days, 5 hours, 6 minutes"
into an integer (suitable for use
for the Uptime, and equivalent,
modules). Available suffixes are:
years
weeks
days
hours
minutes
seconds
Returns
Returns a string representation of the given data (or -1 if an error
occurred). In case of error, the program will croak() with an appriopriate message.