Use the current exception handler during shutdown

It's possible that a different exception handler is defined than the
default `Kohana_Exception::hander`.

Refs #4627
Update the license url, fixes #4778
Avoid division by zero
Follow up to 3bc535eb536e54451b722da9699d052c863ac1b4, determine the download mime by the extension rather than the actual download file (which will probably not exist). Refs #4344

refs #4592

Conflicts:
	classes/kohana/response.php
Merge branch '3.2/develop' of https://github.com/kohana/core into 3.2/develop
Merge pull request #320 from EvanPurkhiser/fixup/4627-shudown-handler

Use the current exception handler during shutdown

refs #4627
Replaced empty string with zero

Outputing as inline style, so empty string doesn't help
Merge pull request #429 from enov/3.2/bug/3373-profiler-division-by-zero

Bug 3373: Avoid division by zero

refs #3373
Merge pull request #399 from bonzai/3.2/bugfix/4778-update_license_url

Update the license url, fixes #4778