openssl: Fixed a macro so that it compiles with gcc >= 4.2.

openssl:  Fixed a macro so that it compiles with gcc >= 4.2.

ASN1_i2d_bio_of, a macro which we use (indirectly, via yet another
macro) in wvstreams, requires the third parameter to be an unsigned
char *, but calls CHECKED_PTR_OF to provide this argument.  This latter
macro, being generic and used all over the place, actually casts its
result to a (void *), which in gcc 4.2 won't magically auto-expand to
an unsigned char *.  Add a new macro which casts to a desired return
type instead, and make ASN1_i2d_bio_of call said macro.