Counting # dynamic instructions in a benchmark

I just checked in the following patch:

This patch adds a new statistic to LLI which indicates the number of
dynamic instructions executed by the program. With this patch enabled,
you can run LLI like this:

$ cd test/Programs/SingleSource
$ make Output/matrixTranspose.llvm.bc
$ lli -stats Output/matrixTranspose.llvm.bc
Checksum before = 2096128.000000
Checksum after = 2096128.000000
Function int (int, sbyte**)* "main" returned int 0