Revert "std: convert {vec,str}::to_owned to methods."

This fixes the strange random crashes in compile-fail tests.

This reverts commit 96cd61ad034cc9e88ab6a7845c3480dbc1ea62f3.

Conflicts:
	src/librustc/driver/driver.rs
	src/libstd/str.rs
	src/libsyntax/ext/quote.rs