Don't let finfo_open to throw warnings and notices, handle them instead

The issue addressed in #230 fixed the test and remove error suppression operator, but that lead to many notices and warning being thrown when not compatible mime file is provided - see travis output for PHP 5.4+:

    PHP Notice: finfo_open(): Warning: offset `<?php' invalid in /home/travis/build/zendframework/zf1/library/Zend/Validate/File/MimeType.php on line 212
    PHP Notice: finfo_open(): Warning: type `<?php' invalid in /home/travis/build/zendframework/zf1/library/Zend/Validate/File/MimeType.php on line 212
    PHP Notice: finfo_open(): Warning: offset `/**' invalid in /home/travis/build/zendframework/zf1/library/Zend/Validate/File/MimeType.php on line 212
    PHP Notice: finfo_open(): Warning: type `/**' invalid in /home/travis/build/zendframework/zf1/library/Zend/Validate/File/MimeType.php on line 212
    Notice: finfo_open(): Warning: offset `<?php' invalid in /home/travis/build/zendframework/zf1/library/Zend/Validate/File/MimeType.php on line 212
    PHP Notice: finfo_open(): Warning: offset ` * Zend Framework' invalid in /home/travis/build/zendframework/zf1/library/Zend/Validate/File/MimeType.php on line 212
    PHP Notice: finfo_open(): Warning: type `* Zend Framework' invalid in /home/travis/build/zendframework/zf1/library/Zend/Validate/File/MimeType.php on line 212

etc.

This PR store the error in variable for possible later use and somehow backports behavior from ZF2.