[CVS ci] PMC constants

A first patch is in CVS. Imcc now understands the syntax:

   set_p_pc P0, 0     # load PMC constant no. 0

The explicit arguments are necessary to disambiguate

   set P0, 0          # assign integer 0 to P0

This isn't much useful per se, as a compiler/you doesn't know the 
constant index of a PMC constant. Therefore next will be some glue code:

   .const .Sub $P0 = "foo"

which will translate to the "set_p_pc" opcode.

leo