Only copy original request headers when following redirects [fixes #4790]

When following a redirect, the client should not add NULL headers
from the follow_headers list that were not set on the original
request. This prevents problems when requesting URLs that
include an authorization signature calculated from the request URL
and headers.
Update Exception.php
Merge pull request #414 from tmihalik/patch-2

Update Kohana/HTTP/Exception.php docblock
Ref #4802: HTTP_Header not compatible with ArrayObject

HHVM complains about this. The Zend engine silently ignore the bug, probably casting the NULL internally to int 0.

Could not create a test for it, as this works with Zend, but it's fatal in HHVM.
Merge pull request #424 from enov/patch-3

Ref #4802: HTTP_Header not compatible with ArrayObject
Fixed typo in comments for Kohana_View::__toString()
Merge pull request #450 from robbytaylor/bugfix/typo-in-comments

Fixed typo in comments for Kohana_View::__toString()
Merge pull request #401 from acoulton/3.3/bug/4790-extra-headers-on-redirect-follow

Only copy original request headers when following redirects [fixes #4790]
Update license URLs in PHPDoc - Ref: #4821

Found links pointing to old location
of license instead of where they are
now at http://kohanaframework.org/license
Merge pull request #466 from randomecho/4821-update-license-links

Update license URLs in PHPDoc - Ref: #4821