Added `CRADLE_EXCEPTION_GUARD`.

* cradle/scope_guard/exception_guard.hpp: Newly added.
* src/scope_guard/jamfile: Added dependency on `/cradle/src/exception`.
* test/scope_guard/exception_guard_run.cpp: Newly added.
* test/scope_guard/scope_guard_in_class_scope_compile_fail.cpp: Newly added.
* test/scope_guard/scope_guard_in_namespace_scope_run.cpp: Newly added.