Package main binaries now go under cmd, leaving the top level for
similarly-named packages.
I'll be moving a lot of data structures and functions out of the
commands and into common packages.
A future CL will also unify all the "+build whatever" restrictions
into one common build tag, since there will be so much package sharing
coming up. Probably they will become "+build extdep", to indicate that
they have dependencies outside of x/tools.
Change-Id: Idc198e0dfa933b5f5de8f2b581533e8d299d2293
Reviewed-on: https://go-review.googlesource.com/2738
Reviewed-by: Andrew Gerrand <adg@golang.org>
