Support OCLint static checker; do some source cleanup

[cgull]

OCLint is a Clang/LLVM based static analyzer. It is usefully different from other static analyzers and has found worthwhile things.

• The biggest issue it shows is the excess length and complexity of many methods. It discovered 600,000,000 different execution paths through Terminal::Framebuffer::new_frame(), and rightly carps regularly about function length, cyclomatic complexity, and number of paths. Nothing done to fix this...
• It also identified many smaller simplifications that could be done to the code base, some of which are quite worthwhile. I think the best thing it identified was large conditionals in contexts that could be escaped, such as

if (foo) {
  // large block
}
return;

into

if (!foo) {
  return;
}
// large block

and there's some other good simplifications.

This has received a week of heavy use on a trip and seems to be in good shape.