mkdir: suppress multiple errors for non-directory argument

[mknos]

• Previously if running "mkdir -p" and the 1st part of an argument is not a directory, the program would incorrectly call mkdir() on the intermediate paths under it
• If I have a regular file 0, "mkdir -p 0/1/2" would show 3 errors because of mkdir("0/1") and mkdir("0/1/2")
• Restructure the program so ARGV can remain as a list of directories (now we don't need the explanation comment for the old confusing code)
• For -p flag, split directory into parts, calling a create_dir() function for each part
• split_dir() handles the case where the 1st part is not a directory, and drops the sub-directory parts

%touch 0
%perl mkdir -p 0/1/2 00 aa/bb/cc # only one error for 0/1/2 argument
mkdir: cannot create directory '0': File exists

%find 00 aa # everything was created except for 0/...
00
aa
aa/bb
aa/bb/cc

[coveralls]

Pull Request Test Coverage Report for Build 12578806958

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.

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Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 72.464%

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Totals
Change from base Build 12566564471:	0.0%
Covered Lines:	350
Relevant Lines:	483

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💛 - Coveralls

[mknos]

Thanks for the suggestion. I added a new commit which rewrites split_dir() using File::Spec.
I found another test case where subdir creation should bail out: permission denied error when creating parent dir.
create_dir() now returns true on success so the subdir creation can stop on error.
This means split_dir() has no need to do any file tests.
Handle special case where File::Spec adds a leading '' list element for absolute paths.

%perl mkdir -p 0/1/2 /0/1/2 aa/bb/cc 00 # single error for 0/1/2 and /0/1/2 respectively
mkdir: cannot create directory '0': File exists
mkdir: cannot create directory '/0': Permission denied

%find aa 00
aa
aa/bb
aa/bb/cc
00

[briandfoy]

changes: suppress multiple errors for non-directory argument