dot-emacs: Fix C indentation quite a lot.

This change fixes a number of C indentation annoyances:

  * One-line blocks are indented relative to the preceding line.

  * Stuff inside `extern "C" { ... }' isn't indended.

  * The `extern "C" {' line itself /is/ indended.

  * Blocks in macro argument lists are fixed.

  * Macro indentation is fixed.