compile time improvements and tracing

• Improved compilation time performance. 20% drop in compilation time
  has been seen in some test programs.

• Improved the compiler's chance to provide good warning messages
  when values in expectations don't quite the types used in the
  function signature (for example signed/unsigned mismatch.)

• Added support for tracing matching calls. This is an aid when
  doing exploratory tests of legacy code. A trace can often
  drastically reduce the time required to understand how the legacy
  code works.

  To use it, create an object of a tracer type, for example:

  TEST(atest)
  {
    trompeloeil::stream_tracer trace(std::cout);
    // normal test code follows
  }