Python interpreter and Library mis-match causes installation to succeed while `pysparse` is not installed

[chaithyagr]

Currently, in the CMake file here:

pysap/sparse2d/python/CMakeLists.txt

Lines 11 to 18 in 529bce6

	find_package(PythonInterp REQUIRED)
	if(NOT DEFINED PYTHON_LIBRARIES OR NOT DEFINED PYTHON_INCLUDE_DIRS)
	find_package(PythonLibs REQUIRED)
	else()
	message(STATUS "Using Python Lib: ${PYTHON_LIBRARIES}")
	message(STATUS "Using Python Inc: ${PYTHON_INCLUDE_DIRS}")
	endif()
	include_directories(${PYTHON_INCLUDE_DIRS})

There is no check if the python interpreter and python libraries are the same version or not. This miss-match can cause a lot of issues..

As a first step, we can limit the python versions to >= 3.6 here. Most of recent versions can handle backward compatibilities, making this not such a big issue.