the MacPro4,1 has the same smc keyset like the MacPro5,1
use the SMC key "FNum" to read the number of keys

so a macpro with only one cpu lists only 5 fans instead of six like
a macpro with two cpus because the keys for all six fans are
always there even if not all are needed.
Merge pull request #253 from denis2342/master