Fix annoying python package cache update stderr messages detected as error

[MMatten]

E.g.

sys-package-mgr: processing modified jar, 'C:\Program Files\Java\jdk1.6.0_45\jre\lib\resources.jar'
sys-package-mgr: processing modified jar, 'C:\Program Files\Java\jdk1.6.0_45\jre\lib\rt.jar'
sys-package-mgr: processing modified jar, 'C:\Program Files\Java\jdk1.6.0_45\jre\lib\jsse.jar'
sys-package-mgr: processing modified jar, 'C:\Program Files\Java\jdk1.6.0_45\jre\lib\jce.jar'
sys-package-mgr: processing modified jar, 'C:\Program Files\Java\jdk1.6.0_45\jre\lib\charsets.jar'
sys-package-mgr: processing modified jar, 'C:\Program Files\Java\jdk1.6.0_45\jre\lib\ext\dnsns.jar'
sys-package-mgr: processing modified jar, 'C:\Program Files\Java\jdk1.6.0_45\jre\lib\ext\localedata.jar'
sys-package-mgr: processing modified jar, 'C:\Program Files\Java\jdk1.6.0_45\jre\lib\ext\sunjce_provider.jar'
sys-package-mgr: processing modified jar, 'C:\Program Files\Java\jdk1.6.0_45\jre\lib\ext\sunmscapi.jar'
sys-package-mgr: processing modified jar, 'C:\Program Files\Java\jdk1.6.0_45\jre\lib\ext\sunpkcs11.jar'

Find out why the package cache priming isn't catching this.