Merge branch 'rs/fsck-duplicate-names-in-trees'

"git fsck" ensures that the paths recorded in tree objects are
sorted and without duplicates, but it failed to notice a case where
a blob is followed by entries that sort before a tree with the same
name.  This has been corrected.

* rs/fsck-duplicate-names-in-trees:
  fsck: report non-consecutive duplicate names in trees

diff --cc fsck.c
Simple merge

diff --cc t/t1450-fsck.sh
Simple merge