Check own display started

[Elias481]

• needed to avoid race conditions when multiple scripts start a X server simultaniously where neighter pre-check will see lock file of the other process not the xdpyinfo check indicates error because he simply rans with X server belonging to different process (see also issue #33)

• currently the python 3 implementation is possibly incomplete as the EasyProcess module currently does not provide a way to inherit the needed fd on path on >= 3.2 --> here the EasyProcess needs to pass eigther "close_fds=False" to subprocess.Popen to re-enable expected previous behaviour of inhereting the fds based on there CLOEXEC mode and/or to allow to pass specific fds to sub-processes via "pass_fds=()" argument of Popen. depending on implementation the display may need to pass the instruction to pass the "displayfd" to EasyProcess...

• possibly this check should be made default, but I want to avoid bad looking failing travis CI checks because of the missing EasyProcess functionality for py3...

[coveralls]

Coverage decreased (-4.9%) to 78.779% when pulling 9164e94f0e96029d837fcb13ca6c9be42475e68f on Elias481:check-own-display-started into 47a20e51e6a82c367b81f7cc2b7777c37365d364 on ponty:master.

[coveralls]

Coverage decreased (-5.04%) to 78.613% when pulling 94d96ee45a210dde7bc55494cb68134f8fad92ea on Elias481:check-own-display-started into 47a20e51e6a82c367b81f7cc2b7777c37365d364 on ponty:master.