patch: standard exit code

[mknos]

• Patch::error() returns $ERROR
• In Patch::print_rejects(), $ERROR is incremented if rejected pieces are found during processing
• No other function updates $ERROR, so Patch::error() indicates if rejects are present
• die() calls are wrapped by an END-block which sets exit code to 1; follow standard and set it to 2 [1]
• Failure to detect a diff in the input is considered an error; call die() to indicate this
• Add EXIT STATUS section to pod as done in other scripts
• test1: "perl patch -x" ---> bad option, exit(2)
• test2: "echo BOGUS-DIFF-123 > bogus.diff && perl patch xargs bogus.diff" ---> no diff found, exit(2)
• test3: "perl patch dirname sort.diff" ---> mismatched diff which can't be applied, exit(1)
• test4: "perl patch a.c correct.diff" ---> diff applies with no failed parts, exit(0)

1. https://pubs.opengroup.org/onlinepubs/007904975/utilities/patch.html

[coveralls]

Pull Request Test Coverage Report for Build 11650380175

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 73.069%

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Totals
Change from base Build 11639173728:	-0.7%
Covered Lines:	350
Relevant Lines:	479

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💛 - Coveralls

[briandfoy]

changes: note that patch exists with 0 for success