Fixed xfail for nbody shootout benchmark by correcting command line parse.
Cleaned up unneeded imports and type changes to resolve compiler warnings.
auto merge of #10410 : willingc/rust/shoot-done, r=huonw

...e.

Cleaned up unneeded imports and type changes to resolve compiler warnings.

Work in process
rustpkg: Eliminate the spurious `os::path_exists(&pkg_src.start_dir.join(p))` assertion failure

This addresses the problem reported in #10253 and possibly elsewhere.

Closes #10253
auto merge of #10342 : catamorphism/rust/rustpkg-dir-checking-and-monitor, r=erickt

r? @brson
io: benchmarks for creation of the various Buffered objects