Minor changes to the build system to build the vm with CSS support
Implementation of the data type CstIntVar.

- Added IntVarLike interface.

CstIntVar and Smallint classes implements the methods from this interface.
Added initial support for builtins that post propagators
Build system modifications
 - Force installation of gecode under lib directory
Merge branch css. Conflicts solved
Changes in order to supoport finite domain variables with the current official virtual machine.
Removed *RichNode self* parameter from CstIntVar.
Finite domain base module is fully functional (FD.int, FD.is, FD.min, FD.max, FD.isIn, FD.value)