Use proper exit codes throughout
Use proper exit codes throughout

We were exiting in a lot of error cases with exit code 0.  Instead,
return something meaning for people who script their use of jipdate.

Signed-off-by: Christoffer Dall <2c58c35362f9f538b58fc30c0db0d1c81cf60d96@cs.columbia.edu>

jbech-linaro/jipdate