ENH: add directive '#sinclude' (or '#includeIfPresent' as long name)

applications/test/dictionary/testDict

...s/utilities/miscellaneous/foamDictionary/foamDictionary.C

src/OpenFOAM/Make/files

src/OpenFOAM/db/dictionary/functionEntries/README

...db/dictionary/functionEntries/includeEntry/includeEntry.C

...db/dictionary/functionEntries/includeEntry/includeEntry.H

...tionary/functionEntries/includeEtcEntry/includeEtcEntry.C

...tionary/functionEntries/includeEtcEntry/includeEtcEntry.H

...tionEntries/includeIfPresentEntry/includeIfPresentEntry.C

...tionEntries/includeIfPresentEntry/includeIfPresentEntry.H

src/OpenFOAM/global/etcFiles/etcFiles.C

src/OpenFOAM/global/etcFiles/etcFiles.H

...se/interFoam/laminar/damBreak/damBreak/system/controlDict