Merge branch 'stable-5.0'

* stable-5.0:
  Use constant for ".lock"
  Simplify locking of FileRepository's index snapshot
  Refactor FileRepository.detectIndexChange()

Change-Id: Ifd427711359bcf38b2c877b2143d45bff0c9895a
Signed-off-by: Jonathan Nieder <jrn@google.com>

diff --cc org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileRepository.java
Simple merge

diff --cc org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java
Simple merge