Create new functions for abstracting header creation and size checking using a use_mini_header flag.
Extending spice header abstraction to inputs.js
Switch to mini header if received from server in common caps
Calling new header on this.sc since functions are not prototype methods
Check for common caps using bitwise operators.  Use mini header, if supported
Adds Mini data header capability detection.  Spice channels will use
mini or full size headers, depending on server capability.  This allows
the client to work with older servers, such as found in the ubuntu preicse
repos.