The current situation of the Gstreamer detection does not always honor
all the configurations set by the user, among this:
- if both WITH_GSTREAMER and WITH_GSTREAMER_0_10 are off, but
  Gstreamer 0.10 is installed in the system, Gstreamer 0.10 support will
  be enable;
- if both WITH_GSTREAMER and WITH_GSTREAMER_0_10 are on, only checks for
  Gstreamer 0.10 will be run.

This patch fixes the Gstreamer detection like this:

  |        -DWITH_...          | Package installed  ||    OpenCV    |
  | GSTREAMER | GSTREAMER_0_10 | gst-1.x | gst-0.10 || gst. support |
  +===========+================+=========+==========##==============+
  |    OFF    |      OFF       |    -    |    -     ||     none     |
  |    OFF    |      ON        |    -    |    no    ||     none     |
  |    OFF    |      ON        |    -    |   yes    ||   gst-0.10   |
  |    ON     |      OFF       |    no   |    no    ||     none     |
  |    ON     |      OFF       |    no   |   yes    ||   gst-0.10   |
  |    ON     |      OFF       |   yes   |    -     ||    gst-1.x   |
  |    ON     |      ON        |   yes   |    -     ||    gst-1.x   |
Signed-off-by: Samuel Martin <s.martin49@gmail.com>