Utility function to make a list from specified amount of objects.

Utility function to make a list from specified amount of objects.
* lisp.h (enum constype): New datatype.
(listn): New prototype.
* alloc.c (listn): New function.
(Fmemory_use_count, syms_of_alloc): Use it.
* buffer.c (syms_of_buffer): Likewise.
* callint.c (syms_of_callint): Likewise.
* charset.c (define_charset_internal): Likewise.
* coding.c (syms_of_coding): Likewise.
* keymap.c (syms_of_keymap): Likewise.
* search.c (syms_of_search): Likewise.
* syntax.c (syms_of_syntax): Likewise.
* w32.c (init_environment): Likewise.
* w32fns.c (Fw32_battery_status, syms_of_w32fns): Likewise.
* xdisp.c (syms_of_xdisp): Likewise.
* xfns.c (syms_of_xfns): Likewise.