High Sierra's APFS cannot use invalid filenames [Bug #13816]

	added workaround for APFS file format.

	  * TestFileExhaustive#test_atime: It fails with nano-sec precise.
	    I changed to use unixtime for this assertion for APFS.
	  * TestFileExhaustive#test_expand_path: skip assertion when given
	    invalid charactor on APFS.

	  [Bug #13816][ruby-core:82383]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@62814 b2dd03c8-39d4-4d8f-98ff-823fe69b080e