Add value cast image morpher.
	
	* tests/value_cast.cc: New.
	* tests/Makefile.am: Update.
	* oln/morpher/value_cast.hh: New.
	* oln/Makefile.am: Update.
	* oln/morpher/internal/image_value_morpher.hh (lvalue): Change
	definition mode from single_vtype to vtypes.



git-svn-id: https://svn.lrde.epita.fr/svn/oln/trunk@647 4aad255d-cdde-0310-9447-f3009e2ae8c0