Complete quoting for parameters of some CMake commands

[elfring]

Some parameters (like "${Boost_INCLUDE_DIR}" and "${CMAKE_SOURCE_DIR}/export/") are passed to CMake commands in your build scripts without enclosing them by quotation marks. I see that these places will result in build difficulties if the contents of the used variables will contain special characters like semicolons.

I would recommend to apply advices from a wiki article.