Convert author and comment on demand.
This sppeds up reading commits a lot by only store the byte
array data when reading commits. For the eclipse plugin I only
need the tree to filter out which commits to display and I can
take the cost of converting the comments to string for the
very few commits to display. Only the displayed commits are actually
converted so this results in convertig author and comment information
for about five commits rather than 20,000 (in my repo).
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>