Attempt to make progress on PR39727/PR45023 blocking migration
to 2.4.  Provide DeflateAlterETag directive to choose between 
2.2 behavior, 2.4 behavior, or dropping ETag from the compressed
representation.

Preserves 2.4 default which breas 304 responses for compressed content.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1586542 13f79535-47bb-0310-9956-ffa450edef68