Add command line options for dpi change

WIP status for lp:inkscape/0.92.x branch:

1) Inkscape 0.92.1pre0 includes a command line option to disable fixing baseline spacing of text in legacy documents:
   --do-not-fix-pre-92 Prevents automatic fix of pre-92 files on opening them.

   https://bazaar.launchpad.net/~inkscape.dev/inkscape/0.92.x/revision/15338

2) The latest patch (pending for 0.92.1pre1) in bug #1659229 includes:
   --do-not-fix-pre-92 Prevents automatic fix of pre-92 files on opening them.
   --dpi-update-method=[none|scale-viewbox|scale-document]
                         Method used to convert pre-.92 document dpi, if needed.

The command line options in (2) currently only support GUI mode (i.e. not yet to be combined with command line options that do not require the GUI). The patch needs to be "forward-ported" to trunk (if accepted for the stable release branch).

On 2017-01-29 03:33 (+0100), Bryce Harrington wrote on the 'inkscape-devel' mailing list:
> Since both --do-not-fix-pre-92 and --dpi-update-method relate to
> the same underlying issue, I bet they could be sensibly combined
> into a single commandline option.
https://sourceforge.net/p/inkscape/mailman/message/35632831/

I do not agree to merge these two different command line options into a single one:
* Auto-fixing baseline spacing of text in legacy files is a [yes|no] decision. The default (and recommended) action is to always apply the fix when opening a file detected as "legacy". There might/will be (rare) cases where it is necessary to allow to disable these changes when opening a legacy file.
* Whether or not a file requires to be adapted for the interal 90->96 dpi change, and which internal method then should be used, depends on the individual file's content and use case (screen, output to device where physical size in absolute "real" units matters), and is not related to the issues with baseline spacing.
None of the factors to decide about the action with regard to document scale affect the decision whether or not to auto-fix baseline spacing.

The only common factor of the two options is that they concern legacy files. Otherwise, they are not related.

Ok I stand corrected, however it reinforces my point that --do-not-fix-pre-92 needs renamed. That is too easily confused with what the dpi update is doing (evidenced at least by the fact that I was confused by it.) I recommend something like --no-convert-text-baseline-spacing that will be exceedingly clear. I don't think the option itself needs to mention the file version; that is a detail that can be reserved to the help text.

`gimp --help` shows that the "--no-XXX" phrasing is an established convention for them.

Btw. the new command line command for not fixing baselines is missing in trunk, as far as I can see. New report?

Hackmann wrote:
> the new command line command for not fixing baselines is
> missing in trunk

Cannot confirm: it was 'forward-ported' in rev 15481:
https://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/15481

$ inkscape -V
Inkscape 0.92+devel r15498
$ inkscape --help | grep text-baseline
      --no-convert-text-baseline-spacing Do not fix legacy (pre-0.92)

Mmh. Thank you, su_v - I didn't try it out, I only compared the files and couldn't find the command... must have overlooked. Sorry!

fix ported to trunk r15729.

The dpi change commandline option isn't documented in the Inkscape man page yet (only in the Wiki release notes and here). Should it be?
https://gitlab.com/inkscape/inkscape/blob/0.92.x/man/inkscape.pod.in