#46 fix uninitialized readline_shutdown

[Anssi Hannula]

new_table->readline_shutdown is not initialized in lib/ss/invocation.c:ss_create_invocation().
This causes lib/ss/invocation.c:ss_delete_invocation() to crash if no readline was found (and thus readline_shutdown remained uninitialized).

We encountered this in Mandriva since readline is now at libreadline.so.6, which is not listed in DEFAULT_LIBPATH in readline.c, and thus not loaded. Quick testing with "SS_READLINE_PATH=libreadline.so.6 debugfs" seems to make the readline functionality work, but I didn't really check what is the actual difference between .so.5 and .so.6.

[Anssi Hannula]

fix uninitialized readline_shutdown