test: make rundir match compiledir/errorcheckdir.

This allows test/dwarf to be supported by run.go.

Update issue 4139.

R=golang-dev, bradfitz, iant
CC=golang-dev
https://codereview.appspot.com/7064067
test: adapt old-style tests to new flag parsing.

The -I. syntax now needs a space to be recognized in the
compiler.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/7098046