ZF-4163: Zend_Cache_Frontend_Page - page cache is not saved when
'memorize_headers' option is set   When 'memorize_headers'
option is set, page content cannot be saved. So second request
to cached content always returns empty string.  There is a typo
in 'Zend/Cache/Frontend/Page.php' in line 304:   First
'strolower' should be changed to 'strtolower'.   commited in
trunk and 1.6 SVN branch (thanks)