always propagate input errors to exit code

always propagate input errors to exit code

Improve robustness in automated system when using exit code in shell scripts,
by exiting with code 2 if there was any input error (even overriding other
possible error exit codes).
Exit code 2 is already used to indicate system errors.

Without the patch:
   $ jq . no-such-file ; echo $?
   jq: no-such-file: No such file or directory
   0

With the patch:
   $ jq . no-such-file ; echo $?
   jq: no-such-file: No such file or directory
   2

Signed-off-by: Nicolas Williams <nico@cryptonector.com>