commit 4632bce35e3854aef5da912c6cefa9768f03937c
author Todd Wang <toddw@google.com> Thu May 07 16:12:17 2015 -0700
committer Todd Wang <toddw@google.com> Thu May 07 16:12:19 2015 -0700
tree 7c33d604907f1cdcc984d2b259460470261f6f8b
parent 151095d1039bafaf505802f511838dbc58a28d2d

lib: Add x/lib/cmdline2 and x/ref/lib/v23cmd.

The cmdline2 package is very similar to the existing cmdline
package.  The main differences:
* Uses Runner interface, rather than Run func.
* Exposes Parse and ParseAndRun, rather than Init/Execute
* Passes *Env to runners, rather than *Command.

The purpose of these changes is to make it possible to get the
ordering of initialization right in our command line tools that
rely on v23.Init.  In particular, the previous Init/Execute API
was bad, since Execute perfomed both arg parsing and command
running.  That made it hard to inject special-purpose code,
e.g. for intializing the v23 context in tests.

The v23cmd package is a very small utility package that builds on
top of cmdline2 to make it really easy to add commands that need
a v23 context to be initialized.

The combination of these two packages lets us get rid of the
global gctx variable used in many of our cmdline tools.  I've
updated most tools that used gctx, to make sure the new mechanism
is really good enough for our needs.

I'll make another sweep in separate CLs to convert all other
tools over to cmdline2, and then have mechanical CLs to replace
cmdline with cmdline2.

Addresses some of vanadium/issues#407

MultiPart: 1/2

Change-Id: Ic277bbc2d930730117188afed891c9b5e26cd8e7