Abort if we try to open a file more than once via filerec_open().

Signed-off-by: Mark Fasheh <mfasheh@suse.de>
Abort if we try to leave dedupe_extent_list() with a non-empty open files
list.

Signed-off-by: Mark Fasheh <mfasheh@suse.de>
Fix too many file descriptors error during dedupe

new_dedupe_ctxt() wasn't properly limiting the number of files we would try
to dedupe at a time. As a result, large lists of duplicate extents would
queue too many files per pass and get EMFILE from filerec_open().

Fix this by setting the correct value of ctxt->max_queable.

Signed-off-by: Mark Fasheh <mfasheh@suse.de>