debian/dpkg-doc.postrm: Use doc-name instead of file-name

debian/dpkg-doc.postrm: Use doc-name instead of file-name
dselect/pkgdisplay.cc: Replace empty string for eflags to a space so gettext doesn't use the translation-info
po/update.sh: Generate dselect/helpmsgs.{cc,h} so we can translate them.
po/POTFILES.in: add dselect/helpmsgs.cc
dselect/pkgtop.cc: use ACS_HLINE instead of `-'
dselect/baselist.cc: change colour of column headings
dselect: add a new --export mode which suppresses the display of the helpscreen