A "ls-files" that emulates "find" to enumerate files in the working
tree resulted in duplicated Makefile rules that caused the build to
issue an unnecessary warning during a trial build after merge
conflicts are resolved in working tree *.h files but before the
resolved results are added to the index. This has been corrected.
* jc/make-dedup-ls-files-output:
Makefile: dedup list of files obtained from ls-files