Merge pull request #2006 from jersey99/signed-in-rtlil-wire

Preserve 'signed'-ness of a verilog wire through RTLIL

diff --cc frontends/ast/genrtlil.cc
Simple merge

diff --cc frontends/ilang/ilang_parser.y
Simple merge

diff --cc kernel/rtlil.cc
Simple merge

diff --cc kernel/rtlil.h
Simple merge