* xterm.c (xim_initialize): Always pass a copy of resource name

* xterm.c (xim_initialize): Always pass a copy of resource name
to XRegisterIMInstantiateCallback and eassert whether return
value is True.  Passing copy is important because Xlib doesn't
make its own copy and resource name argument usually points to
SSDATA (Vx_resource_name), which may be changed from Lisp.
(xim_close_display): For XUnregisterIMInstantiateCallback,
always eassert return value and pass exactly the same values
as were used for XRegisterIMInstantiateCallback.  Otherwise
XUnregisterIMInstantiateCallback will always fail.  See Xlib
sources to check why if you are interested.