Completely broke sc_lib.

I changed the way library is probed for tokens/certificates. "sc_lib" is now used only for authentication purposes.
I introduced a few new functions (and modified some old ones) in sc.c(h), so that library is initially probed  for all available tokens and certificates that user can choose from them.
SC doesn't work right now in pageant. I will rewrite it to support multiple PKCS#11 libraries, with all available certificates listed.