Machines are limited to so much energy per tick

regardless of source of energy
Merge remote-tracking branch 'upstream/master'
Don't attempt to receive energy if none is required
Fix Slaughterhouse blacklist
Reduce default requested energy to 35 MJ
Use machine.getActivationEnergyMJ() instead.
I will eventually get this right
Merge pull request #238 from skyboy/master

Manage energy better