Clear stale code and format style for SrcLineMap

The source line mapping pass was cleaned.
Clean and un-comment the print slice code

The code to print static and dynamic slice was commented once before. We
now uncomment it since it's the final answer we'd like to get. It seems
that the unit tests can be passed.
Format the TraceFile coding styles
Pass a stream to DynValue::print

This makes the print function more usable for different output streams.
Print the slice to -slice-file (default stdout)

Previously we dump it to stdout directly, which is not recommended.
Use -trace-file command line for trace file name

Previously there are two command lines for the trace file name. Now we
use the external variables to reduce the redundant code. Note that the
same command line argument of LLVM pass can not be defined twice.
Ignore the *.slice files
Set the DEBUG_TYPE for giri and giri-util