commit 3e4aded87161e7684f1e48fbffaeb9c3e0df3d8e
author Todd Wang <toddw@google.com> Tue Mar 01 17:51:56 2016 -0800
committer Todd Wang <toddw@google.com> Tue Mar 01 17:51:56 2016 -0800
tree b3b390edbfa086f2eb7c1ef7ec55be1eefc60797
parent d25b44bdfa233c2f7bb79ae6f1973bc8ddd25689

lib: Use lookpath package consistently.

Changes the signature of the lookpath functions to:
Look(env map[string]string, ...) (string, error)
LookPrefix(env map[string]string, ...) ([]string, error)

The env map is passed in, rather than a slice of dirs, to
facilitate supporting other platforms in the future.  E.g. on
windows we need to consult both the PATH and PATHDIRS environment
variables.

We now return an error, to more closely match LookPath in
os/exec.  The implementation of these methods has also changed,
to more closely match the os/exec implementation.

Also removed the copy of LookPath in runutil, and changed code to
use the lookpath package instead.

Fixes v.io/i/1157

MultiPart: 3/3
Change-Id: I3890f4debd8d519dc8d86eb4eed6759d9f6fd18e