Let SSL_CIPHER_description() allocate the buffer for the description,
rather than passing in a fixed size buffer.

This is yet another example of a horribly designed API - if the given
buffer is NULL then SSL_CIPHER_description() allocates one for us (great!),
which we then need to free (no problem). However, if this allocation fails
it returns a pointer to a static string "OPENSSL_malloc Error" - obviously
bad things happen if we call free() with this pointer.

Unfortunately, there is no way of knowing that the function failed, other
than comparing the returned string against the string literal - so do that
before calling free()...

Joint work with beck@ during g2k14.