libXt: Changes to 'master'

[Jon TURNEY]

Rebased ref, commits from common ancestor:
commit 171d82fa36bb601360da2cc519718c46f137c467
Author: Jon TURNEY <jon.turney at dronecode.org.uk>
Date:   Tue Apr 14 12:21:58 2015 +0100

    Include unistd.h for getpid()
    
    Signed-off-by: Jon TURNEY <jon.turney at dronecode.org.uk>
    Reviewed-by: David Macek <david.macek.0 at gmail.com>

commit af9c277491c9bdc37a6fc5ae5a6c6ca190bfa56c
Author: Jon TURNEY <jon.turney at dronecode.org.uk>
Date:   Tue Apr 14 12:19:07 2015 +0100

    Include direct.h header for _getdrives() on Win32
    
    Signed-off-by: Jon TURNEY <jon.turney at dronecode.org.uk>
    Reviewed-by: David Macek <david.macek.0 at gmail.com>