Use known length of a Lisp string to copy it faster.

Use known length of a Lisp string to copy it faster.
* lisp.h (lispstrcpy): New function.  Add comment.
* callproc.c (child_setup):
* dbusbind.c (xd_append_arg):
* doc.c (get_doc_string):
* font.c (Ffont_xlfd_name):
* frame.c (xrdb_get_resource):
* process.c (Fmake_network_process, network_interface_info):
* w32fns.c (Fx_open_connection):
* w32proc.c (sys_spawnve):
* xfns.c (select_visual):
* xfont.c (xfont_list):
* xsmfns.c (x_session_initialize):
* xterm.c (x_term_init): Use it.