Nohup and glob

[henryiii]

This patch adds two things:

1:
I've added a NOHUP modifier, working on both local and ssh_machines. It unifies the syntax for the two machines and makes it easier to use. The classic methods of doing this, local.daemonic_popen and ssh_machine.nohup are still supported for compatibility. As part of the patch, minor cleanup was done on execution modifiers class structure. The nohup modifier is a little like bash syntax:

>>> local['sleep'][1.234] & NOHUP

vs.

>>> nohup sleep 1.234 & 

It defaults to nohup's std output, but can use new output files and "/dev/null" too, and can append or replace. It even respects > and >> on the command it is applied to.

Like bash's nohup, it disconnects from the process started, even if the current process/shell is exited.

2:
Added support for globbing with a list. You can now do:

>>> local.cwd // ('*.tar.gz', '*.zip')

And get a list of items that match both globs. This helps make up for the fact that that python's glob module doesn't support the '{}' syntax of bash.