`-bindtop`/"Bind Top"
- DPD: add top boundary (width 3X) by default, using new
BARCODE_BIND_TOP; "relabel" option; some compliance checks
- GUI: only skip encoded/errored signal processing if active modal
ExportDialog (wasn't clearing/setting error text bar correctly
for DataDialog)
- CODE128: debug print checksum
- CODE49/DATAMATRIX/QR/ULTRA: fix uniqueness of errtxt nos
- manual: fuller DPD doc; some spelling typos, formatting
