Fix `cargo run` for renamed bin targets
auto merge of #421 : alexcrichton/cargo/issue-418, r=wycats
Remove all subcommand executables

This commit removes all distributed executables except for `cargo`. All
builtin subcommands are implemented through library calls, and the fallback
methods are retained to maintain extensability through new subcommands.

Closes #393
auto merge of #420 : alexcrichton/cargo/issue-393-2, r=brson

This commit removes all distributed executables except for `cargo`. All
builtin subcommands are implemented through library calls, and the fallback
methods are retained to maintain extensability through new subcommands.

Closes #393
Implement cargo-package

This command will assemble the current package into a tarball ready for
uploading to the cargo registry. Currently no further verification is done
beyond packaging the local repository into a tarball, but in the future this
could execute other operations such as api stability tools.