Merge pull request #228 from agtorre/2.4dev

Merging updates from master to 2.4dev
Move fileid map in SMF_Writer to SmallFileFD

So that only the file id mapping entries for open files are cached
in memory.
Merge pull request #230 from zhang-jingwang/2.4dev

Move fileid map in SMF_Writer to SmallFileFD