Avoid undefined behavior in signed left shift.

Avoid undefined behavior in signed left shift.

This ports to GCC 4.9.0 with -fsanitize=undefined.
* alloc.c (bool_vector_fill, SETMARKBIT, UNSETMARKBIT):
* data.c (Fash):
* regex.c (extract_number):
* lisp.h (make_number, XINT):
Do not shift a 1 bit left into a sign bit.
* alloc.c (struct cons_block, struct float_block): Use unsigned,
not int, for gcmarkbits.  All uses changed.