[2.4.x] Merge r1931452, r1931453 from trunk

[notroj]

core: Add millisecond support to ErrorLogFormat time specifiers

%{m} prints the timestamp in millisecond-resolution.

* include/util_time.h:
  Define new AP_CTIME_OPTION_MSEC option for printing time in milliseconds
  format.

* server/util_time.c (ap_recent_ctime_ex):
  Handle AP_CTIME_OPTION_MSEC to print time in a millisecond format.

* server/log.c (log_ctime):
  Recognize the m time option in both fast-path and composite %{...}t formats.

Submitted by: Luboš Uhliarik <luhliari redhat.com>
Github: closes #597



* server/log.c (log_ctime): Fix syntax error in r1931452
  (added by me when tweaking whitespace, not from the PR author).