True size option removes any origin offset present in input

[scruss]

## Summary

`-t` (*Show true HPGL size* option) removes any origin offset in both
**hpgl** and **nc** output modes. This does not seem to be documented.

* This is an upstream bug in Debian

* This has also been reported to the developer, Martin Kroeker.

## Versions tried

V 3.4.4 (Ubuntu 20.04.1 LTS x86_64)

also affects current Debian version and development version at
http://ruby.chemie.uni-freiburg.de/%7Emartin/

## Sample input

A square of side 100 mm, with origin at (20, 20) mm, in file
`test-square2.hpgl`:

    SP1;SP1;PA;PU800.000000,800.000000;PD4800.000000,800.000000;PD4800.000000,4800.000000;PD800.000000,4800.000000;PD800.000000,800.000000;SP0;

## Command line

    hp2xx -t -m hpgl -f - test-square2.hpgl

## Expected output

Identical to input, that is: a square of side 100 mm, with origin at
(20, 20) mm:

    SP1;SP1;PA;PU800.000000,800.000000;PD4800.000000,800.000000;PD4800.000000,4800.000000;PD800.000000,4800.000000;PD800.000000,800.000000;SP0;

## Received output

A square of side 100 mm, with origin shifted to (0, 0) mm:

    SP1;SP1;PA;PU0.000000,0.000000;PD4000.000000,0.000000;PD4000.000000,4000.000000;PD0.000000,4000.000000;PD0.000000,0.000000;SP0;

## Comments

hp2xx has likely shown this behaviour for a very long time. While the
output plot is *technically* true size, relocating the origin to zero
removes any margins present in the source file. This means that hp2xx
is not currently useful as a register-true filter.

Given that as many users likely depend on this behaviour as are
confounded by it, it might be sufficient to document that this is how
hp2xx works by default. Ideally, an option to retain origin offsets
should be added.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: hp2xx 3.4.4-11
ProcVersionSignature: Ubuntu 5.4.0-59.65-generic 5.4.78
Uname: Linux 5.4.0-59-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.14
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Wed Jan 13 12:28:19 2021
InstallationDate: Installed on 2019-07-31 (532 days ago)
InstallationMedia: Ubuntu 19.04 "Disco Dingo" - Release amd64 (20190416)
SourcePackage: hp2xx
UpgradeStatus: Upgraded to focal on 2020-05-09 (249 days ago)