Merge r1523484,1523505,1523613,1523844,1523853,1524014,1524031,1529515 from trunk

Essentially: The sendfile test is now simple to automate, and runs
             automatically from the autoconf-based build's "make check".

r1523484:

Hard-code the same address family on the server side as it already
is on the client side; otherwise, connect will fail on dual-stack
if IPV6_V6ONLY defaults to ON.

(The socket setup could stand to be rewritten!)

r1523505:

Allow sendfile-as-client to start up the server program
and display its output.

r1523613:

report an error if the client couldn't read stdout from the server within a couple of seconds

r1523853:

client mode: wait a bit for the server to start up if
it was spawned by the client (to solve buildbot failure,
presumably)

axe stray "aprerr" emit from aprerr()

r1524014:

fix what is effectively apr_time_from_msec(apr_time_from_msec(small))

Reported by: Yann Ylavic <ylavic.dev gmail.com>

r1524031:

follow-up to r1523853 and r1524014:
  when running in automated mode (client starts the server process),
  make the client stop calling apr_connect() as soon as it works or
  some non-ECONNREFUSED error occurs

Submitted by: Yann Ylavic <ylavic.dev gmail.com>

r1523844:

run the sendfile test automatically (autoconf-based build)

r1529515:

Fix executable file extension on Windows (autoconf-based build)


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/branches/1.5.x@1531116 13f79535-47bb-0310-9956-ffa450edef68