Fix handling filenames with trailing whitespace, update test

[h3xx]

This stems from a (bug? feature?) in IO::File which allows complex file handle modes and stuff to be indicated in the filename, e.g. '>file.txt' or '| cat file.txt'. Specifying the file open mode disables this parsing.

This also fixes the issue where attempting to add files using Archive::Tar (via add_files()) with trailing whitespace would fail with Unable to add file: 'foo ' at ./myscript.pl line 24..

Closes #10 (GitHub)
Closes https://rt.cpan.org/Public/Bug/Display.html?id=103279

[h3xx]

I'll submit another PR to fix the Windows test.

I'm having a hard time repro-ing it using the version of Perl that ships with Git for Windows ("This is perl 5, version 34, subversion 0 (v5.34.0) built for x86_64-msys-thread-multi"). In this version everything works fine in the test as-written.

I've noticed some funny bugs in Windows systems regarding whitespace; if you create a file programmatically with a trailing space, Windows Explorer will not be able to delete the file or move it, saying "item not found." The file properties dialog will pull up with all the timestamps blank and the Security tab with an error message. File names with leading whitespace work as-expected.

tl;dr Windows is mildly allergic to filenames with trailing spaces.