[#30790] Correct spelling of the X-Frame-Options header on Joomla 2.5

#### Steps to reproduce the issue
1. Open the Joomla back-end log-in page (www.example.com/administrator/)
2. Using browser tools (e.g. the Firefox web console), check headers received with server response to GET www.example.com/administrator/

#### Expected result
2. "X-Frame-Options: SAMEORIGIN" is received

#### Actual result
2. "X-Frames-Options: SAME-ORIGIN" is received

#### System information (as much as possible)
PHP 5.3.6 on Apache on Linux

#### Additional comments
What should be server header "X-Frame-Options: SAMEORIGIN" is sent as "X-Frames-Options: SAME-ORIGIN" on Joomla 2.5.24. (I.e. both, header name AND its value are misspelled.)

Note: This was fixed on "master" with http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=30790, but not on Joomla 2.5.x.