Allow plugins to have native dylib dependencies

Ensure that the dynamic linker search path contains the location of the output
directories for these dependencies when compiling with plugins.

Closes #597
Fix building with current rustc
Fit text within window in Safari when under 629px in width
auto merge of #627 : dotdash/cargo/rustup, r=alexcrichton
auto merge of #632 : EduardoBautista/cargo/fix-width-in-safari, r=alexcrichton

Text is not responsive under 629px in Safari.
auto merge of #617 : alexcrichton/cargo/issue-597, r=brson

Ensure that the dynamic linker search path contains the location of the output
directories for these dependencies when compiling with plugins.

Closes #597
Remove the deprecated -u flag

This flag has been deprecated in favor of `cargo update` for quite some time
now.