//Format of FreeSegments record, release 3.02.06. It is never compressed.
//It is probably not accessed by its key, but from its offset given in the file header.
// ----------TKey---------------
// byte 0->3 Nbytes = Number of bytes in compressed record (TKey+data) TKey::fNbytes
// 4->5 Version = TKey class version identifier TKey::fVersion
// 6->9 ObjLen = Number of bytes of uncompressed data TKey::fObjLen
// 10->13 Datime = Date and time when record was written to file TKey::fDatime
// | (year-1995)<<26|month<<22|day<<17|hour<<12|minute<<6|second
// 14->15 KeyLen = Number of bytes in key structure (TKey) TKey::fKeyLen
// 16->17 Cycle = Cycle of key TKey::fCycle
// 18->21 SeekKey = Byte offset of record itself (consistency check) TKey::fSeekKey
// 22->25 SeekPdir = Byte offset of parent directory record (TFile) TKey::fSeekPdir
// 26->26 lname = Number of bytes in the class name (5) TKey::fClassName
// 27->.. ClassName = Object Class Name ("TFile") TKey::fClassName
// 0->0 lname = Number of bytes in the object name TNamed::fName
// 1->.. Name = lName bytes with the name of the object <file name> TNamed::fName
// 0->0 lTitle = Number of bytes in the object title TNamed::fTitle
// 1->.. Title = lTitle bytes with the title of the object <file title> TNamed::fTitle
// ----------DATA---------------
// 0->1 Version = TFree class version identifier TFree::Class_Version()
// 2->5 fFirst = First free byte of first free segment TFree::fFirst
// 6->9 fLast = Byte after last free byte of first free segment TFree::fLast
// .... Sequentially, Version, fFirst and fLast of additional free segments.
// .... There is always one free segment beginning at file end and ending before 2000000000.