add PRINTD to printutils.cc
add PRINTD to printutils.h
add '--debug=' option to openscad cmdline. see printutils.h for usage
add global OpenSCAD::debug string to printutils.cc (see printutils.h for usage)
replace logstream with PRINTD / PRINTDB . add boost include to printutils.cc
fix PRINTD to PRINTDB
Merge branch 'unstable' into printd0
Added --debug to usage
Merge branch 'unstable' of github.com:openscad/openscad into unstable