If both Python 2 and Python 3 are found, then build bindings for both of
them during the build process.  Currently, one version of Python is
detected automatically, and building for the other requires changes the
CMake config.

The largest chunk of this change generalizes OpenCVDetectPython.cmake to
find both a Python 2 and Python 3 version of Python.  Secondly, the
opencv_python module is split into two modules, opencv_python2 and
opencv_python3.  Both are built from the same source. but for different
versions of Python.

It may be an arbitrary string, and, for example, in Ubuntu 13.10
it's set to "2.7.5+", which breaks the find script.

Aligned strings in CMakeList

Modified the check on plantuml extension

Some fixes

Moved find_host_program for plantuml script

Who knows, maybe the user's Sphinx installation uses a Python we couldn't find.

Most importantly, added support for multiple include directores,
but also did some general cleanup.

Rationale: we already depend on it (e.g. some scripts use print_function).

None of this should be relevant as of CMake 2.8.7.

On my MacOS the output of the sphinx-build binary is the following:

Error: Insufficient arguments.

Sphinx v1.2b1
Usage: /usr/local/bin/sphinx-build [options] sourcedir outdir [filenames...]

...

I have installed sphinx, but without this change HAVE_SPHINX==0 for me, so I can't build docs.

In these cases, just using print() is enough to ensure py2/3
compatibility.

This also fixes the bug where the Sphinx version gets detected as
"Sphinx vX.Y.Z" instead of "X.Y.Z" on Unix-like systems.

 [~] Automatically tracked dependencies between modules
 [+] Support for optional module dependencies
 [+] Options to choose modules to build
 [~] Removed hardcoded modules lists from OpenCVConfig.cmake, opencv.pc and OpenCV.mk
 [+] Added COMPONENTS support for FIND_PACKAGE(OpenCV)
 [~] haartraining and traincascade are moved outside of modules folder since they aren't the modules