Round the timestamp returned from the filesystem.
MSys (wndows) only return second precision timestamps for files even though
NTFS uses precision down to 1/100th of a second. Since jgit cannot handle
most of the file attributes in the index I want to use the higher precision
whenever possible. So jgit now compares the timestamp at the millisecond
precision returned by Java, but if an index entry does not use the subsecond
bits those are not compared against.
Git itself seems not to use the subsecond part for comparison so jgit will
store millisecond timestamps.
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>