google test finds python undermining ability to find python you want about blt

[cyrush]

Here is the strategy I am using:

################################################################
#! guard against google test's unconditional hunt for python
################################################################
if(DEFINED PYTHON_EXECUTABLE)
    set(_pyexe_guard ${PYTHON_EXECUTABLE})
endif()

set(CMAKE_DISABLE_FIND_PACKAGE_PythonInterp TRUE)
set(CMAKE_DISABLE_FIND_PACKAGE_Python TRUE)
#!##############################################################

################################################################
# init blt using BLT_SOURCE_DIR
################################################################
include(${BLT_SOURCE_DIR}/SetupBLT.cmake)

################################################################
#! guard against google test's unconditional hunt for python
################################################################
set(CMAKE_DISABLE_FIND_PACKAGE_PythonInterp FALSE)
set(CMAKE_DISABLE_FIND_PACKAGE_Python FALSE)

if(DEFINED _pyexe_guard)
    set(PYTHON_EXECUTABLE ${_pyexe_guard})
    unset(_pyexe_guard)
endif()

Setting CMAKE_DISABLE_FIND_PACKAGE_ZZZ isn't sufficient: PYTHON_EXECUTABLE gets cleared when those are set.

[cyrush]

Grumble, even this isn't sufficient.

[cyrush]

resolved in #679