Complete quoting for parameters of some CMake commands

[elfring]

Some parameters (like "${SOCI_SOURCE_DIR}/core" and "${CMAKE_INSTALL_PREFIX}/lib") 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 spaces.

I would recommend to apply advices from a Wiki article.

[Krzmbrzl]

Paths should be consistently quoted once #1118 is merged.