Reinstate bn_isqrt.c r1.8 and crypto_lock.c r1.3

Reinstate bn_isqrt.c r1.8 and crypto_lock.c r1.3

This traded local copies of CTASSERT() to the one in crypto_internal.h.
This change was backed out due to SHA-512 breakage on STRICT_ALIGNMENT
architectures still using Fred Flintstone's gcc without asm sha512.

Original commit message:

Use crypto_internal.h's CTASSERT()

Now that this macro is available in a header, let's use that version
rather than copies in several .c files.

discussed with jsing