STYLE: make dictionary error more descriptive (#1065)

src/OpenFOAM/db/dictionary/dictionary.C

src/OpenFOAM/db/dictionary/dictionaryCompat.C

src/OpenFOAM/db/dictionary/dictionaryIO.C

src/OpenFOAM/db/dictionary/dictionarySearch.C

src/OpenFOAM/db/dictionary/dictionaryTemplates.C

src/OpenFOAM/db/dictionary/entry/entry.C

src/OpenFOAM/global/argList/argList.C