Complete test suite overhaul.

* rename a few test modules to make the names more consistent

* do not copy/use Sphinx from build/ (unnecessary without 2to3)

* use a temporary dir for *all* test projects, the source tree
  will stay pristine that way  (default is tests/build)

* speed up tests by ~3x by splitting up test projects and avoiding
  rebuilds

Makefile

@@ -48,10 +48,10 @@ reindent:
 	@$(PYTHON) utils/reindent.py -r -n .
 endif
 
-test: build
+test:
 	@cd tests; $(PYTHON) run.py -d -m '^[tT]est' $(TEST)
 
-covertest: build
+covertest:
 	@cd tests; $(PYTHON) run.py -d -m '^[tT]est' --with-coverage \
 		--cover-package=sphinx $(TEST)