Merge from Dependencies branch (nmap-exp/patrick/dependencies)

with modifications from [2].

** Short description from [1] **

I have created a patch to NSE that replaces runlevels with a table of
dependencies that clearly outlines what other scripts the script
depends on. The table is of the form:

dependences = {"script1", script2", ...}

Runlevels become an internal representation of the order of scripts
that are generated by the dependencies. Dependencies only enforce
an execution order and not a requirement for execution.

[1] http://seclists.org/nmap-dev/2009/q4/295
[2] http://seclists.org/nmap-dev/2009/q4/446

scripts/banner.nse

@@ -13,7 +13,6 @@ increase in the level of verbosity requested on the command line.
 
 author      = "jah <jah at zadkiel.plus.com>"
 license     = "See Nmap License: http://nmap.org/book/man-legal.html"
-runlevel    = 1
 categories  = {"discovery", "safe"}