In most cases (e.g. any of the nmap.socket operations), functions can
take full host and port tables instead of just host.ip and port.number.
This makes for cleaner-looking code and easier extensibility if we
decide to check for a protocol on both TCP and UDP, for instance.
In addition to fitting better (brute library is the verb, creds library
is the noun), this will allow creds.lua to use creds.Account internally
where necessary (see subsequent commits)
Also change old references to string argument "OPEN" into
creds.State.VALID.
* replace require function calls with stndse.silent_require
* fixed a bug in nse_main that would fail creating scripts.db when a script
fails to load
* reworked some code to provide limited functionality even though SSL is not
present