apk upgrade -U should upgrade apk-tools first

If new packages depend on new apk-tools, they’ll fail to install. For now, a workaround is:

apk update
apk add -u apk-tools
apk upgrade

(from redmine: issue id 140, created on 2009-08-18, closed on 2011-03-24)

• Changesets:
  • Revision 59d222d5 by Timo Teräs on 2011-01-01T13:48:10Z:

upgrade: perform upgrade of apk-tools first if available

Also re-exec's apk-tools to perform rest of the upgrade using
the new apk-tools. This allows handling of new apk-tools features
properly. Fixes #140.