Fix incorrect network prefix in Java Meterpreter

Apparently, getNetworkPrefixLength can return -1, which confuses the Ruby
side. Therefore fall back to guessing the prefix in this case, as we do it
for Java <= 1.6.
Improved docs and partial specs for Rex::Text

Conflicts:
	lib/msf/core/modules/loader/base.rb
	lib/rex/poly/block.rb
	lib/rex/text.rb
Clean up all the whitespace found
Land #1756, @wchen-r7's cleanup of spaces
Add module for US-CERT-VU 345260
Add bins for #1748
Land #1748, fix for java meterp network prefixes

[Closes #1748]