Fix CMake whitespace

Applied a two-space indent. It was a mixture of 2, 3, 4 and 8 space indents and tabs; I don't know how you could look at it without going crazy. I mostly used Vim's "=" command, even in cases where its output is potentially controversial, because at least it's consistent.

Also modified vertical whitespace in a couple of places. A whitespace-insensitive diff will show you where.