Due to the fact that -cover injects additional code to the original
source, tests run with -cover will often have incorrect line numbers.

Also includes docs for -list regexp missed by ba8ff87d

Updates #6329

Change-Id: I87f0618ac31e96071bca61055cc17c0cbdee208a
Reviewed-on: https://go-review.googlesource.com/38640Reviewed-by: Rob Pike <r@golang.org>