[dunecontrol] comma in suggestions list breaks tracking of implicit dependencies and locations are not properly appended to cmake flags

The situation was as follows:

• pdelab suggests alugrid
• duneuro uses pdelab
• pdelab adds alugrid to the list of libs to link
• duneuro fails to build, as it didn't find alugrid, but tries to link to it

The problems was an erroneous suggestion entry in dune-pdelab (see pdelab/dune-pdelab!575 (merged)). This syntax error was not detected but lead to an inconsistent consideration of dune-alugrid in different modules.

Solution: properly check the dune.module syntax in dunecontrol.