Update FormHelper.php

disabled multiple checkbox input should not generate an enabled hidden input,
as it leads to saving empty data upon submission -> carrying the disabled attribute to the hidden input prevents this
fixing testcases + do not disable the hidden input on partial disables
Merge pull request #4975 from ptica/disabled-hidden-input

Disable the hidden input for multi checkbox inputs when inputs are disabled.
Add additional useful tests for autoLink()

These new tests cover an important case that could easily be missed in
the future. Links with URL's should not be re-linked.

Refs #4998
Relative paths should be created relative to pwd.

If create() is called with a relative directory and the path does not
exist, it should be created inside of the folder->pwd() and not inside
the process' cwd.

Refs #4990
Merge pull request #5001 from cakephp/issue-4990

Relative paths should be created relative to pwd.