Changes:
* Removed the apkindex_files cache. That particular cache caused
bug #189 and didn't bring any real-world performance improvements
(tested 3x with that cache and 3x without, no significant speed
difference). I decided to remove it instead of keeping it/adding
even more code to resolve the bug.
* Fix the check for already built packages: always use the architecture,
that the package should be built for instead of the architecture of
the build environment (e.g. use armhf, even when building a noarch
package in the x86_64 chroot). This partially resolves#341.
* Make pmb.chroot.apk.install_is_necessary() more robust: If the binary
package is missing, although it should be there, print a warning and
build it with force.
21c09b3b3c