thus reduced IO load when creating a table.
Uncompressed abbreviated segment and dicts aren't affected by
this b/c CS'es system catalog uses uncompressed dict files. CS
now doesn't work with empty dicts files.
for extent extention.
Added a getter, moved some methods from protected into public to use
with unit tests, e.g createFile, setPreallocSpace. Added code stub in
FileOp::oid2FileName to use with UT.
Add more comments.
Changed return value for HDFS'es fallocate.
Removed unnecessary code in ColumnBufferCompressed::writeToFile
Replaced Nulls with Empties in variable names.
