Lots more DSGraph tests

I have checked in a directory called test/DSGraphs, with one
subdirectory for each of the test cases in
test/Programs/{Single,Multi}Source/. Running gmake in test/DSGraphs
will generate DS graphs for each of the programs for which the bytecode
for the original program exists. This includes graphs for a number of
large benchmarks, such as the SPEC codes that currently have bytecode