Make gtest output more silent, ninja issue #528.

This is just a proof-of-concept. The terminal printing logic should be
extracted from src/build.cc and then reused here.
move single-line printing to new class
refactor; no intended functionality change
move printing of new lines into LinePrinter.
Make LinePrinter members private, add comments.
Use LinePrinter in test runner.
Make ninja_test output nicer.
Try to fix build on Linux.
Try to fix build on Linux more.
Merge pull request #532 from nico/sshhh_gtest

Make test runner less chatty.