Extcap Capture Interface

 Extcap is a plugin interface, which allows for the usage
 of external capture interfaces via pipes using a predefined
 configuration language which results in a graphical gui.

 This implementation seeks for a generic implementation,
 which results in a seamless integration with the current
 system, and does add all external interfaces as simple
 interfaces.

 Windows Note: Due to limitations with GTK and Windows,
 a gspawn-winXX-helper.exe, respective gspawn-winXX-helper-console.exe
 is needed, which is part of any GTK windows installation.

 The default installation directory from the build is an extcap
 subdirectory underneath the run directory. The folder used by
 extcap may be viewed in the folders tab of the about dialog.

 The default installation directory for extcap plugins with
 a pre-build or installer version of wireshark is the extcap
 subdirectory underneath the main wireshark directory.

 For more information see:

  http://youtu.be/Nn84T506SwU
  bug #9009

 Also take a look in doc/extcap_example.py for a Python-example
 and in extcap.pod for the arguments grammer.

 Todo:
   - Integrate with Qt - currently no GUI is generated, but
     the interfaces are still usable

Change-Id: I4f1239b2f1ebd8b2969f73af137915f5be1ce50f
Signed-off-by: Mike Ryan <mikeryan+wireshark@lacklustre.net>
Signed-off-by: Mike Kershaw <dragorn@kismetwireless.net>
Signed-off-by: Roland Knall <rknall@gmail.com>
Reviewed-on: https://code.wireshark.org/review/359
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>