ZXID: Fixed some build issues.

One use of parent_storage() was missed when the API was changed.

Some places where missed when the precompiler started prefixing
symbols with the module name.
ZXID: More build fixes.

Missed a few spots...
Fix bug where the write callback could be dropped if 0 bytes were written.
Whitespace changes.
Clean up the init/exit of auto_bignum_program code.
No need to cleanup auto_bignum_program twice. It's also done in Gmp module, where it is set.
auto_bignum_program is always set when pike code is running.
Refactor away the hook_in_gmp_funcs, now that Gmp is a static module.
Removed bignum include.
Removed get_auto_bignum_program_or_zero
ZXID: Some support for ZXID 1.19 and later.

Some fields in struct zxid_conf changed names in ZXID 1.19:2013-12-04.
Removed prototypes for removed functions.
Use bignum_program instead of auto_bignum_program.
Access bignum_program directly.
Remove get_auto_bignum_program
Move INT64 check into bignum.h for reduce_stack_top_bignum.
push_longest is not better than push_int64. int128 doesn't work, as an example.
string_from_bignum wasn't used, and just a proxy for digits.
Inlining is_bignum_object is both faster and smaller.
Simplify code.