Put -L paths from scripts are in LD_LIBRARY_PATH

Like the old build command, this commit adds support for executables run by
cargo (and tests) to ensure that `-L` paths for a dynamic library are added to
LD_LIBRARY_PATH after a compilation is run.

Closes #915
Don't require a manifest for `cargo owner` commands
Fix the root output directory when cleaning examples

This forgot to take into account the logic from some other locations, so I added
a helper method!

Closes #912
Add a `search` command to cargo
auto merge of #959 : jakub-/cargo/cargo-search, r=alexcrichton

This will currently call out to the registry service. In the future it may be sensible to add package descriptions to the git index so that search can be done offline.

Closes https://github.com/rust-lang/cargo/issues/925.
auto merge of #918 : alexcrichton/cargo/issue-912, r=brson

This forgot to take into account the logic from some other locations, so I added
a helper method!

Closes #912
auto merge of #919 : alexcrichton/cargo/issue-915, r=brson

Like the old build command, this commit adds support for executables run by
cargo (and tests) to ensure that `-L` paths for a dynamic library are added to
LD_LIBRARY_PATH after a compilation is run.

Closes #915
auto merge of #936 : alexcrichton/cargo/issue-923, r=brson

Closes #923