Land #4143, @kernelsmith's get_custom_exe fix

* Initializes the exe variable
* Fixes #4131
Remove redundant rb-readline from Gemfile

MSP-11585

The entry in the gemspec is sufficient.
Don't depend on 'rb-readline' on Windows

MSP-11585

`rb-readline` gem doesn't work with Ruby Installer for 1.9.3 because of
`NoMethodError undefined method 'dlopen' for Fiddle:Module`.  Removing
`rb-readline` may be a temporary fix it if turns out that this is a bug
with rb-readline or some other upstream bug.
Address Juan's points
Update metasploit-framework-full.gemspec

Fix typo
Add support for the getsid command

There has been Meterpreter work done as well to support this. But this
commit allows for a new 'getsid' command which tells you the sid of the
current process/thread. This can be used for things like determining
whether the current process is running as system. It could also be used
for golden ticket creation, among other things.
touch up lib/rex/mime/message.rb
touch up visual_mining_netcharts_upload
Land #4139, Visual Mining NetCharts

landed after some touch up
Land #4149, readline adjustments

* Windows guard, DRYing
Add full disclosure URL
Better method name

Should be srvhost, not lhost
Fix #4089 - undefined method `downcase' for nil:NilClass
Land #4148, @wchen-r7 fixed #4133
Land #4151, downcase nil deref. fix
No more than 100 columns on description
Use built-in format for RPORT
Reduce code complexity
Use fail_with
Delete unnecessary nil comparision