Re-indent all C files to 4 spaces

[elric1]

The idea here is to make things a lot closer to what clang-format produces in a couple of steps so that each patch is easy to evaluate. To review this:

:; git fetch --all
:; git checkout elric1@four-spaces
:; git log -p -b -1

Note that the diff is empty which means that all of the changes are only to whitespace. -b is not greedy as it only considers multiple whitespace to be equivalent to a single space rather than -w which ignores the lot.