SETCIRCUITPURPOSE's format in the control spec is misleading

From the control spec...

 761 3.11. SETCIRCUITPURPOSE
 762 
 763   Sent from the client to the server.  The format is:
 764       "SETCIRCUITPURPOSE" SP CircuitID SP Purpose CRLF
 765 
 766   This changes the circuit's purpose. See EXTENDCIRCUIT above for details.

And from 'EXTENDCIRCUIT above'...

3.10. EXTENDCIRCUIT
 736 
 737   Sent from the client to the server.  The format is:
 738       "EXTENDCIRCUIT" SP CircuitID
 739                       [SP ServerSpec *("," ServerSpec)]
 740                       [SP "purpose=" Purpose] CRLF

This seems to imply that "SETCIRCUITPURPOSE 4 controller" is valid, but, it isn't, "SETCIRCUITPURPOSE 4 purpose=controller" is.

 764       "SETCIRCUITPURPOSE" SP CircuitID SP Purpose CRLF

should be...

 764       "SETCIRCUITPURPOSE" SP CircuitID SP "purpose=" Purpose CRLF

I'm attaching a git formatted patch which makes this modification.