Sync with trunk

- class pair -> struct pair
- BugFix: Do not try to build installed modules.
- BugFix: Better detection of installed modules in dunecontrol.
- BugFix: Allow specification of modules reachable only via pkgconfig
  when using duneproject.
- BugFix: Use correct linker flags when using global and local installations
  of DUNE.


[[Imported from SVN: r6742]]