Log Message:
net/coturn: Merge (minor) improvements from wip

(There is also wip/coturn, from which net/ was apparently imported.  I
didn't realize net/coturn existed,, and had improved wip
significantly, and Adam made mostly-independent improvements to net/,
probably not realizing wip/coturn existed...  This is of the start of
fully merging back to just net/ with all the improvements.)

  - reword DESCR and COMMENT based on upstream site
  - take coMAINTAINERSHIP, to be changed to MAINTAINER after mail I
    sent to the MAINTAINER times out
  - fix rcsid in rc script
  - add comment about disabling the stringop warning; it's not clear
    that this isn't masking bugs

(Overall, this commit does nothing impactful.)