Anything that frees or reallocates struct form_state must now call the
new functions ecmascript_detach_form_state or ecmascript_moved_form_state.
These functions should then clear out any dangling pointers, but that has
not yet been implemented.
Add ecmascript_interpreter.backend_nesting, increment it when
beginning to evaluate an expression, and decrement it when evaluation
finishes. Then assert that it is zero in ecmascript_put_interpreter.
This detects bug 957 and similar ones before they corrupt memory.
Replace the ECMAScript module initialisation and de-initialisation
routines that wrapped the SMJS and SEE module initialisation and
de-initialisation routines by having the module system call the SMJS
and SEE routines its own darned self.
