Revert "Capture only coverage data for the current project in the first place, instead of extracting it from all coverage data in a second step. This seems to be needed as extraction spuriously might fail in some cases."

This reverts commit ce14dcd0.

Reason for the revert: The change did not work on Ubuntu 12.04 due to an old version of lcov.

Capture only coverage data for the current project in the first place, instead of extracting it from all coverage data in a second step. This seems to be needed as extraction spuriously might fail in some cases.