Add a root_app property to `cli.Application`. Closes #140

This adds a property to `cli.Applicatino callled root_app which returns a
reference to the "root" Application object in a tree of Application objects.

Conflicts:
	plumbum/cli/application.py
Changelog: update for 1.4.2 and the upcoming 1.4.3
copy: mkdir of the destination file's parents. closes #146
Pipeline: fail command when source process fails. closes #145
oops: forgot a print statement there
Path: add encoding option to read/write. closes #148
Path: filter now accepts a second predicate for recursing into directories. closes #147
Preparing for v.1.4.3
fix test for python 3.2 compat
cosmetic fixes
remove ConcreteCommand.machine
Adding ConcurrentCommand (experimental). closes #151
Adding cluster to experiments
Parallel: Added ClusterSession, and allowed args in popen
Merge pull request #152 from koreno/parallel

Parallel updates: Added ClusterSession, and allowed args in popen