Remove docs that shouldn't be built
Always generate a lockfile with dev-dependencies

Previously an invocation of `cargo build` would generate a lockfile *without*
dev dependencies, but an invocation of `cargo test` would generate a lockfile
*with* dependencies. This causes odd problems and diffs with the lockfile.

This commit switches the resolve-to-be-a-lockfile to using all dependencies of a
package, while the resolve-to-be-compiled continues to use just the dependencies
needed for the current build.
More import renaming fallout
auto merge of #402 : alexcrichton/cargo/import-rename, r=alexcrichton
auto merge of #375 : wycats/cargo/doc-fewer-things, r=alexcrichton
auto merge of #389 : alexcrichton/cargo/dev-dependency-lockfile, r=wycats

Previously an invocation of `cargo build` would generate a lockfile *without*
dev dependencies, but an invocation of `cargo test` would generate a lockfile
*with* dependencies. This causes odd problems and diffs with the lockfile.

This commit switches the resolve-to-be-a-lockfile to using all dependencies of a
package, while the resolve-to-be-compiled continues to use just the dependencies
needed for the current build.
Don't build docs/tests into separate dirs

This commit changes the hash of Profile to only take into account
flags/variables that affect the actual output file itself (as opposed to its
location), and then changes cargo {test, build, doc} to all use the same
directory of output (in order to share deps).

This will cause a `cargo build` to remove all of the tests generated by `cargo
test`, but it speeds up the cycle of `cargo test` followed by a `cargo build` by
not needing to rebuild all dependencies.

Additionally, `cargo bench` now shares the same directory as
`cargo build --release` for the same reasons as above.

Closes #348