grep: sprinkle catfile()

[mknos]

• Copy the code pattern from bin/du when running grep in recursive mode
• Joining directory entry names with catfile() is likely more portable
• I didn't test this patch on windows, but grep works the same with patch applied on my linux system, e.g. "perl grep -r grep ."

[coveralls]

Pull Request Test Coverage Report for Build 10001624961

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.7%) to 76.268%

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Totals
Change from base Build 9997088738:	-0.7%
Covered Lines:	376
Relevant Lines:	493

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💛 - Coveralls