sendmsg

<< obj { executable array } sendmsg >>
When obj is in k-class (i.e. obj is of the form 
 [<<class.Context>> , body ]), then the CurrentContextp is changed
to <<class.Context>> and the obj <<executable array>> will be executed.
If not, CurrentContextp is changed to the PrimitiveContextp and
the obj <<executable array>> will be executed.
cf. setcontext, newcontext, StandardContextp, system_variable,
    sendmsg2, primmsg, supmsg2.