Not use fixed path for valgrind in Makefile

Just replace "$(HOME)/pyston_deps" with "$(DEPS_DIR)" to make things
keep going well when the dependencies are placed elsewhere.
Merge pull request #33 from mjisyang/develop

Not using fixed path for valgrind in Makefile
Rudimentary importing support

Doesn't handle packages or anything other than importing a .py file
(ex zip import, .so, .pyc), but has some basic support for
sys.path and sys.modules.