Use float instead of Lisp_Object for rehash_size

Use float instead of Lisp_Object for rehash_size

* src/alloc.c (purecopy_hash_table):
* src/fns.c (maybe_resize_hash_table, Fmake_hash_table):
(Fhash_table_rehash_size):
* src/lisp.h (struct Lisp_Hash_Table.rehash_size):
The rehash_size member of struct Lisp_Hash_Table is now a
float, not a Lisp_Object.
* src/alloc.c (purecopy_hash_table): Assign members in order.
* src/fns.c (make_hash_table): Use EMACS_INT for size and
float for rehash_size, instead of Lisp_Object for both.
All callers changed.
* src/lisp.h (DEFAULT_REHASH_SIZE): Now float, not double,
and 1 smaller.
* src/print.c (print_object): Simplify by calling
Fhash_table_rehash_size and Fhash_table_rehash_threshold.
Avoid unnecessary NILP.