auto_test_package() stops on failure

[mbojan]

auto_test_package() calls test_dir() which uses stop_on_failure = TRUE by default. The function exits in case of errors while it should not but keep monitoring the source tree.

[mbojan]

Would you like a separate PR or append #1212 ?

[hadley]

Just append please.

[mbojan]

Appended. This can be closed as soon as #1212 is merged.