find -mtime [+-n]" is broken  (behaves as "-mtime n")

find -mtime allows to find file according to their age. However, this version interprets -mtime -n and +n in the same way. But it should interpret find -mtime -n as finding files that are *strictly less* than n days old and find -mtime +n as finding files that are *strictly more* than n days old.

Lets say we created one file each day in the last 3 days in directory tmp:
$ mkdir tmp
$ touch tmp/a -t $(date --date="today" +"%y%m%d%H%M")
$ touch tmp/b -t $(date --date="yesterday" +"%y%m%d%H%M")
$ touch tmp/c -t $(date --date="2 days ago" +"%y%m%d%H%M")
$ touch tmp/d -t $(date --date="3 days ago" +"%y%m%d%H%M")

If we run the following, we would expect this output
$ ./find tmp -mtime -2
tmp
tmp/a
tmp/b

However, I actually get this output
$ ./find tmp -mtime -2
tmp/c

Results are the same if I replace -n with +n, or just n (in which case the results are correct).
