Destroy the mutex when finish tracing in atexit()
Improve the start of slice code

Now we rely on the -start-slice command line to know the start of slice
function name and instruction count number. If this option is not
provided, we treat the first return instruction of main function as the
start of slicing point.
Simplify the code of source line mapping
Simplify the basic block numbering
Add start-slice file for unit test4
Clean the Makefile under test

The old Makefile to generate the report was renamed to
Makefile.diagnosis for back up.