SERVER-9335: move cap.cpp with namespace_details
SERVER-9335: remove dead code from NamespaceDetails
SERVER-9335: some notion of interface is there now
SERVER-9335: don't call getCollection from NamesapceDetails
SERVER-9335: remove addRecordToRecListInExtent and allocateSpaceForANewRecord from pdfile
SERVER-9335: madvise sequenetial for all capped collections
SERVER-12310: add parallelCollectionScan command
SERVER-9335: fix dbtests with new alloc code