Implement execute_calle.
Merge branch 'dev' of github.com:flavioc/meld into flavio-dev

Conflicts:
	vm/exec.cpp
	vm/external.cpp
	vm/program.cpp
Back port custom external functions.
Merge branch 'dev' of github.com:flavioc/meld into flavio-dev

Conflicts:
	vm/external.hpp
	vm/program.cpp