Our upstream-built release tarballs already contain many unversioned
paths and so will never overlap with another version of CMake in the
same installation prefix. Therefore we do not need a versioned name for
the documentation directory. Configure our release binaries to place
the documentation in an unversioned directory so that one can use the
same path to refer to the documentation locally even after updating
CMake. For example, on OS X one may see the documentation in
`/Applications/CMake.app/Contents/doc/cmake/html/index.html`.
Disable the CMake_INSTALL_DEPENDENCIES option by default and turn it on
explicitly in our packaging scripts. This simplifies packaging in
distributions that provide the dependencies for us without having to
install them. We only need 3rd-party runtime dependencies to be
installed for packaging with redistributable binaries.