Log Message:
Fix for security/opensc regression

When security/opensc was updated to 0.23.0, it gained a
--enable-notify configure flag.

The feature adds a libopensc dependency on libglib, which in turns
brings libpthread into the game.

When using the opensc-pkcs11.so module with a non threaded program
such as ssh(1), libopensc will load some thread-enabled glib function
that attemps to initialize pthread stuff. That would require libpthread
to be linked in, and if it is not the case, module load aborts.
Here is the crash in action:

Program received signal SIGABRT, Aborted.
0x000072403899c46a in _lwp_kill () from /lib/libc.so.12
(gdb) bt
#0  0x000072403899c46a in _lwp_kill () from /lib/libc.so.12
#1  0x0000724038849223 in __libc_thr_create_stub () from /lib/libc.so.12
#2  0x0000724036a9c3ee in ?? ()
#3  0x0000000000000000 in ?? ()

This change turns the notify feature into a disabled by default
option so that opensc-pkcs11.so can work agan with ssh(1).