Guard against overflow in `codemap::span_to_lines`.#25013

Merged

bors merged 2 commits intorust-lang:masterfrom

pnkfelix:span_to_lines-oflo

May 7, 2015

Commits on May 4, 2015

Avoid latent (harmless) overflow in core::slice.
pnkfelix
committed

Commits on May 5, 2015

Guard against overflow in `codemap::span_to_lines`.
pnkfelix
committed