This allows too turn it on for work without an additional patch.
Also fix a bug in the disable code - when the SVG is enabled,
allow to select SVG files.
SVG import need some refinements to be efficient, so it is disable for v 5.x.
Will be re-enabled later.
Enabling SVG import is *only* for developers, not for users.
* Do not compile dxf old files.
* import gfx, gal mode: make absolute placement working.
* Import gfx in legacy canvas: use it and make interactive placement working
* Take imported line width in account. Ensure DXF line thickness is OK.
* handling empty files in legacy mode.
jean-pierre charras
John Beard
Seth Hillbrand
Maciej Suminski