LWS_SERVER_OPTION_DO_SSL_GLOBAL_INIT to default to runtime ssl disable

https://github.com/warmcat/libwebsockets/issues/468



Adds lws_check_opt() to regularize multibit flag checking.

There's a new context creation flag LWS_SERVER_OPTION_DO_SSL_GLOBAL_INIT,
this is included automatically if you give any other SSL-related option flag.
If you give no SSL-related option flag, nor this one directly, then even
though SSL support may be compiled in, it is never initialized nor used for the
whole lifetime of the lws context.

Conversely in order to prepare the context to use SSL, even though, eg, you
are not listening on SSL but will use SSL client connections later, you can
give this flag explicitly to make sure SSL is initialized.

Signed-off-by: Andy Green <andy@warmcat.com>