apache_request_headers need not go through recapitalization of incoming
headers and should be pass through as is.
This is a follow up on #2107 (c82b57b) by @danhunsaker;
#2409: Updated based on feedback by @narfbg;
See #2409: Remove double replacing of dashes and instead change `Content-Type` to `CONTENT_TYPE`
See #2409: Reformating and code cleanup for request_headers;
#2409: Force Content Type to go through camelization;
See #2409: Avoid overwriting global $_SERVER and set Content-Type to protected property;
Merge pull request #2409 from chernjie/develop

apache_request_headers need not go through recapitalization of incoming headers