Also: OG compiler debug info for foreach iterator changed to match actual variable name
Adds:
- ast/DebugStatementMarker: for "intrusive debug" (ecompile -i) instructions
- codegen/DebugBlockGuard: pushes and pops debug block #
- format/DebugStoreSerializer: writes .dbg and .dbg.txt files
- representation/DebugBlock: holds parent block # and local variable names for each block
- representation/DebugStore: holds all debug information
