Logging enhancements and apache24 updates

[sosherof]

• Added additional logging statements.
• Removed all #ifdef _DEBUG around existing logging statements, allow LogLevel to decide.
• Code now inserts an input header "X-SENDFILE-INVOKED" before making a subrequest. The sub-request can cause mod_rewrite to fire a second time. The header allows a RewriteCond to be used to skip any rules that should not re-apply.
• Replaced code that inserts the requested file into buckets with the newer apr_bridge_insert_file command, which properly handles large files.
• Replace code that empties the incoming brigade with apr_brigade_cleanup, which does the same thing but in one command.
• Added APLOG_USE_MODULE statement to allow module level logging.