Fix #2836
[ci skip] AND -> &&
Righting a wrong in the Session library

 - Change userdata(), flashdata(), tempdata() to return all the respective data when no parameter is passed.
 - Revert the addition of all_flashdata().
 - Deprecate all_userdata().
 - Fix related changelog entries that were all inconsistent.
Add &newline; and &tab; to CI_Security::
CI_Security: Add 'form' and 'xlink:href' to evil attributes
Fix syntax errors
CI_Security: Add <select> and <keygen> tags to the list of 'naughty' HTML elements
CI_Security: Also add <svg> to 'naughty' HTML elements
[ci skip] Add a link to PHP bug 54709 in is_really_writable()'s docblock
Partially fix #2667
Re-add 'on\w*' to evil attributes (rel #2667)