Update pyramidsegment to inherit from GstOpencvVideoFilter instead of from
GstElement. This means less code and more uniformity with other OpenCV
elements.
The opencv element includes were full of duplicates and uneeded headers.
For example a few elements that stopped using gstcvopencvutils still
included that header file.
With the switch of gstopencv.c to C++, all OpenCV elements are built with
g++. The template variable clashes with C++'s feature of the same name.
Rename template to templ to avoid any clash.
If old opencv1-style legacy include directory is available,
this change becomes purely cosmetic (maybe will compile a bit faster).
It becomes an FTBFS fix when opencv1-style include directory is missing
(possibly because opencv package maintainer decided not to pack it).
https://bugzilla.gnome.org/show_bug.cgi?id=747705
AC_CHECK_HEADERS() calls action-if-not-found also if just one of
the headers checked for is missing, which is not what we wanted.
Also, check for highgui_c.h instead of highgui.hpp.
https://bugzilla.gnome.org/show_bug.cgi?id=672226
Where highgui.h doesn't exist any more, but only opencv2/highgui/highgui.hpp.
Also, not quite sure why we're checking for cvaux.h, it's not used anywhere.
