FIX: Coverity defects + removed some implicit type conversions

These Coverity-Warnings were actually pretty misleading. It turned out, that I changed the signature of `Spooler::Process` from `Process(std::string path, std::string base_path)` to `Process(std::string path, bool allow_chunking)` without changing the calls to this methods.

`spooler->Process(entry.GetUnionPath(), "data")` implicitly casted the `const char*` to `bool`. Uhargh.

Additionally I fixed some implicit constructions of `SpoolerDefinition` and made the constructor of `SpoolerDefinition` *explicit*.