merge r1363186 from trunk:

#define AP_MAX_SENDFILE 16777216  /* 2^24 */

/**

 * Special Apache error codes. These are basically used

 *  in http_main.c so we can keep track of various errors.

 *        

 * MPM child process exit status values

 * The MPM parent process may check the status to see if special

 * error handling is required.

 */

/** a normal exit */

#define APEXIT_OK		0x0