unpack-trees: don't update files with CE_WT_REMOVE set

unpack-trees: don't update files with CE_WT_REMOVE set

Don't update files in the worktree from cache entries which are
flagged with CE_WT_REMOVE.

When a user does a sparse checkout, git removes files that are
marked with CE_WT_REMOVE (because they are out-of-scope for the
sparse checkout). If those files are also marked CE_UPDATE (for
instance, because they differ in the branch that is being checked
out and the outgoing branch), git would previously recreate them.
This patch prevents them from being recreated.

These erroneously-created files would also interfere with merges,
causing pre-merge revisions of out-of-scope files to appear in the
worktree.

apply_sparse_checkout() is the function where all "action"
manipulation (add, delete, update files..) for sparse checkout
occurs; it should not ask to delete and update both at the same
time.

Signed-off-by: Anatole Shaw <git-devel@omni.poc.net>
Signed-off-by: David Turner <dturner@twopensource.com>
Helped-by: Duy Nguyen <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>