configure: Let the user enable both built-in protocols and purple
There's no real risk in enabling these, since protocols/purple/purple.c already avoids adding duplicate protocols in purple_initmodule():
/* If we already have this one (as a native module), don't add a libpurple duplicate. */ if( find_protocol( prot->info->id ) ) continue;
/* If we already have this one (as a native module), don't
add a libpurple duplicate. */
if( find_protocol( prot->info->id ) )
continue;