This should allow RequestHeader statements to be passed to a vhost. This can either be a single string or and array of statements.

More detail on RequestHeader declarations can be found here:
http://httpd.apache.org/docs/2.2/mod/mod_headers.html#requestheader
fixing typos.
apache::mod{'headers':} is needed by both RedHat and Debian.
request_headers is usually an array, so use a plural variable name
Added comments for request_headers
Created the class apache::mod::headers to specifically handle mod_headers. This will automatically be enabled if the request_headers parameter is defined when calling apache::vhost
_requestheader.erb now rejects empty arrays, and skips empty strings in arrays.

an array of empty strings ['',''] will still include the fragment, but no RequestHeader rules, which should be safe.
Add request_header docs, specs, and refactor template
Merge pull request #25 from hunner/requestheader_hunner

Add RequestHeader support to apache::vhost