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
Add a `harness` manifest option

This option is used to disable the --test flag to rustc for a test or benchmark
target in order to signal that the binary already knows how to run the testing
infrastructure.

The test/benchmark is still compiled and run as usual, and the exit code is
expected to reflect the result of the test/benchmark.

Closes #431