pgsql: Use BIO functions to avoid passing FILE * pointers to OpenSSL

Log Message:
-----------
Use BIO functions to avoid passing FILE * pointers to OpenSSL functions.
This fixes potential crashes on old versions of OpenSSL and the requirement on
"Applink" in new versions when building with MSVC and using different
runtimes.

Dave Page with fixes from me.

Modified Files:
--------------
    pgsql/src/interfaces/libpq:
        fe-secure.c (r1.94 -> r1.95)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-secure.c?r1=1.94&r2=1.95)