Improve information in Palaso stack traces

To get stacktraces that show the line numbers the pdb/mdb
files need to be next to the assemblies.

- always download pdb/mdb files, even for release builds
- copy pdb/mdb files to output directory
- rearrange order of targets in mkall.targets so that downloading
  shows up before copying.

Change-Id: Ib322dad388ad5dd79ad9a4923f65e0e501dde749