compile: BuildOrder: properly handle local dependencies.

- Dependencies outside of the currently compiled package are still
  ignored.
- Before there was a bug that resulted in ignoring imports via
  includes.
- Use TSort from the standard library.
- It turned out that yast2-network contains dependency cycles
  between includes and modules. They can be safely broken.
fixups according to review: better message; Array.delete
report *which* file has an invalid byte sequence

happens with author names in latin-1 when parsing files for
dependencies
Merge pull request #68 from mvidner/build-order

compile: BuildOrder: properly handle local dependencies.