Add a reserve call to the stack data structure.

This allows the caller to guarantee that there is sufficient space for a
number of insertions without reallocation.

The expansion ratio when reallocating the array is reduced to 1.5 rather than 2.

Change bounds testing to use a single size rather than both INT_MAX and
SIZE_MAX.  This simplifies some of the tests.

Switch the stack pointers to data from char * to void *

Reviewed-by: Andy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4386)