fwnull: use a debug build on 'make distcheck'
fwnull: mass substitution lw -> loc

... and 'const struct cl_loc *' -> TLoc
fwnull: use TOperand instead of 'const struct cl_operand'
fwnull: move some typedefs to global scope
fwnull: include the intra-block state into Data
fwnull: split the analysis into two phases

1) fixed-point computation
2) emission of diagnostic messages