- libavcodec issue
- some decoders alter AVCodecContext width/height values, in a wrong way
- eg. in issue 2815, vp6f decoder changes these values, resulting in distorted / invalid frames
- this patch forces default AVCodecContext values

* removed OpenGLFuncTab, now extensions are loaded internally
* added support of GlBuffer and GlTexture2D to InputArray/OutputArray
* added ELEMENT_ARRAY_BUFFER and PIXEL_PACK_BUFFER targets
* added copyFrom/copyTo method for GlBuffer and GlTexture2D
* removed GlFont
* removed pointCloudShow
* removed OpenGLCleanCallback
* added Access parameter to GlBuffer::mapHost
* added autoRelease parameter to all create methods

This reverts commit 4abf0b31.

Changes are reverted because they break build of proxy dlls on Windows

Issue #2114

Added test checking that all valid fourcc values are converted properly

This should be safe todo unless we are writing a signal handler.

xioctl() assumes that ioctl takes int request. Cope with
  int ioctl(int d, unsigned long request, ...)
to avoid "invalid argument".

* Decouple Video4Linux2 support from Video4Linux as existence of
  v4l2 on a system does not imply support for v4l.
* Don't use V4L's struct video_window in V4L2 code.
* Removed __USE_GNU as comment says:
      /* support for MJPEG is only available with libjpeg and gcc,
         because it's use libjepg and fmemopen()
  so replace with test for fmemopen() if found necessary.

The video(4) driver provides a Video4Linux2 compatible API for
various video peripherals. This patch propagates HAVE_VIDEOIO if
the sys/videoio.h include file is found, which is the signature of
video(4).

OpenCV issue #2604

After this patch applied an attempt to encode empty images produces exception
saying "Raw image encoder error: Empty JPEG image (DNL not supported)"

when compiled with GStreamer, open (of a file) segfaults.

Fix was suggested by Bostjan Vesnicer.

The change is based on pull request #211.

These codes should be included into regular builds.

- imdecode_() only creates a temporary file when needed.
- Use the string's empty() function to flag if the temporary file needs
to be deleted.