basename: support -- option terminator

[mknos]

• Similar to what was committed for bin/dirname, '--' should be interpreted as the end of options (currently it is taken literally)
• This was found when testing against OpenBSD version
• test1: "perl basename --" --> error, no argument
• test2: "perl basename -x" --> error, bad option
• test3: "perl basename -- -x" --> basename of "-x"
• While here, one call to usage() in bin/dirname was missed

[coveralls]

Pull Request Test Coverage Report for Build 10423928136

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.7%) to 73.069%

---

Files with Coverage Reduction	New Missed Lines	%
bin/units	3	70.77%
<!--	Total:	3		-->

Totals
Change from base Build 10407100403:	-0.7%
Covered Lines:	350
Relevant Lines:	479

---

💛 - Coveralls

[briandfoy]

changes: accept -- as end of options