Add a line about the license of this project.
Remove vgcore.* files at "make clean".
Move the "ENABLE_SAFE" macros out of "ENABLE_DEBUG" section.
Remove debugging prints in deque implementation.

The deque.c is copied (with necessary modification) from HabaneroC. Hence the
debugging prints is not necessary because the code should run correctly.
Bug fix: avoid corrupting stack.

Avoid writing to existing stack when resuming a fiber.