Attach a pty to each node's bash process

This should enable node commands that are expecting a tty to
behave better.
Avoid overhead of another process (env) in startShell()
Don't set self.waiting twice
Possibly faster check for sentinel.
Fix findPid since pty uses \r\n as line ending
Set default printPid back to True
Fix pid regex to eat \r\n
Restore non-mnexec pid detection for background commands
added default controller class
fixed command parameter
set DefaultController as the mininet class default
Clean up standard topologies to use build
restructured defaultController into a function
revised comment on defaultController function
removed bookmark
Check for Controller type using isinstance()
Merge branch 'devel/defaultController' of https://github.com/cdburkard/mininet into cdburkard-devel/defaultController

Conflicts:
	bin/mn
	mininet/net.py
Merge branch 'cdburkard-devel/defaultController'
Merge branch 'master' into devel/pty
Reverting the disable signals change