COMP: Ensure PreventDirWithSpaces CMake variables is passed to inner project.

This commit ensures that spaces can be used in either source or build
directory when configuring Slicer inner project. This is done by passing
down the variable ${PROJECT_NAME}_SKIP_DIR_WITH_SPACES_CHECK

This commit also documents and simplifies usage of
"PreventDirWithSpaces" CMake module.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23360 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Consider inner build dir when checking for max root directory length.

This commit introduces the convenience CMake module "PreventDirWithTooManyChars"
and update code to account for length of the inner build subdirectory.

It means if the maximum length of the top-level build directory is 40,
assuming the inner build directory is "Slicer-build", the check in
the inner build will expect a path of length 53.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23361 3bd1e089-480b-0410-8dfb-8563597acbee