* Simplify size test in PackWriter
* Declare critical exposed methods of ObjectToPack final
* Declare internal flag accessors of ObjectToPack final
* Remove unused method isDeltaAttempted()
* Simplify setDoNotDelta() to always set the flag
* Read .gitmodules config from the tree in SubmoduleWalk
* Add a CommitBuilder method to edit arbitrary DirCacheEntrys
* Add a release() method to SubmoduleWalk