find: reject the deprecated -perm +MODE octal form to match GNU

[AlejandroCoronadoN]

GNU find rejects the deprecated -perm +MODE octal form (a leading + followed by an octal number). uutils silently accepts it: the + is treated as an unknown prefix, so it falls through to an exact numeric comparison and matches files instead of erroring.

$ find . -perm +644 ; echo $?
./f          # wrongly matches
0
$ gfind . -perm +644 ; echo $?
gfind: invalid file mode '+644'
1

Same for +0 and +400. Symbolic forms (+rwx, +u+w) and the 644 / /644 / -644 forms are unaffected. This rejects a leading + followed by a digit, matching GNU.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.29%. Comparing base (955282d) to head (ac5998b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #851   +/-   ##
=======================================
  Coverage   92.29%   92.29%           
=======================================
  Files          35       35           
  Lines        7445     7450    +5     
  Branches      388      389    +1     
=======================================
+ Hits         6871     6876    +5     
  Misses        433      433           
  Partials      141      141           

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[codspeed-hq]

Merging this PR will not alter performance

✅ 20 untouched benchmarks

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_{Comparing AlejandroCoronadoN:perm-plus-octal-reject (ac5998b) with main (955282d)}