tree 5cd8e42fa472feb682d65a682cfc557e94edcb0a
parent 4053f37c2ba5f9edc5a3bf5b844a32d1b7c8e580
author James Robinson <jamesr@chromium.org> 1452549485 -0800
committer James Robinson <jamesr@chromium.org> 1452549501 -0800

Handle unset JIRI_ROOT env variable in jiri script

This is needed to handle this case:
$ export JIRI_ROOT=/something
$ unset JIRI_ROOT

Testing for "${JIRI_ROOT}" results in the following error:
/something/.jiri_root/scripts/jiri: line 41: JIRI_ROOT: unbound variable

The {foo+x} syntax is explained here:
http://stackoverflow.com/questions/3601515/how-to-check-if-a-variable-is-set-in-bash

Change-Id: Ie9d5166ab2c02776ca0ad1b9d10ce8a0e478d40d