Sometimes (e.g. when using an external API), a script wants to connect
by name to a server and doesn't care whether IPv4 or IPv6 is used. By
passing the "any_af" option, the first resolved address of any address
family will be used, allowing external-category scripts which used to
fail with -6 to succeed.
Changes fall into these categories:
1. Avoid pathological string building. Loops over x = x .. "foo" can
become very slow. Instead, use strbuf.lua, table.concat, or just one
continuous concatenation; a = x .. y .. z is one operation, better than
a = x .. y; a = a .. z
2. Use hex-escaped strings instead of string.char. I find this more
readable in many cases, and it avoids a table lookup and function call.
3. Don't duplicate code. A few libraries and scripts had re-implemented
stdnse.generate_random_string or openssl.rand_bytes.
* 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
