Merges branch 'trac3954'

Merge branch 'trac3939'

doc/devel/qa.dox
    Added description of KEA_PIDFILE_DIR

doc/guide/keactrl.xml
    Added discusion of PID files to section 6

src/bin/keactrl/keactrl.in
    start_server()
        Revised wording of already-running log message

Correction of typos/grammatical errors etc.  Also included text in the
contributors' section explaining why test-driven development is used.

src/bin/keactrl/keactrl.in
    - get_pid_from_file() - new function which returns a server's PID from its
    pid file, or 0

    - check_running() - modified to use get_pid_from_file(), sets $_pid and $_pid_file
    globals

    - send_signal() - modified to use get_pid_from_file()

    - start_server() - modified log emitted if server is already running to
    contain the PID and pid file

    - stop_server() - new function to stop a given server, IF it is running.
    reload_server() - new function to reload a given server, IF it is running.

    - get_pids() - deleted

    - Replaced use of send_signal with stop_server or reload_server to provide
    better visual feedback to users.
~

Added #include for waitpid() added to testing by 3769.

Merge branch 'trac3769'