simplify constant usage. FILEINFO_MIME_TYPE is available since PHP 5.3.0
fixed missing const argument, when passed magic_file argument fails.
Merge pull request #4102 from sasezaki/validator_fileinfo_simplify_constants

simplify constant usage. FILEINFO_MIME_TYPE is available since PHP 5.3.0
Merge branch 'hotfix/4102'

Close #4102