minor white-space changes
atomspace: emit TVchanged signal ...

It wasn't being emitted in one obvious location.
migrate from boost::thread to std::thread
Fix a double-signal-emit bug
iAtomspace: expand the test coverage
make the atomsapce test more stressful.
more test expansion
Add test for truth-value changes
test link addition
Merge pull request #364 from linas/master

fix for bug #361