Added a PRCList member and accessors for linking entries on eviction and doom lists.
Moved check for IsStreamBased() from nsCacheEntry::GetData() to nsCacheEntryDescriptor::GetData(), to allow cache devices to set the mData member.
Added checks to nsCacheEntryDescriptor methods to return NS_ERROR_NOT_AVAILABLE if the descriptor is already closed.
git-svn-id: svn://10.0.0.236/trunk@88133 18797224-902f-48f8-a5cc-f745e15eee43
