Most SANE backends store resolution in DPI as an integer value TYPE_INT. Some store it as TYPE_FIXED. Twain always uses TW_FIX32 for resolution.
This MR provide access to the resolution in ICAP_xRESOLUTION and DG_IMAGE/DAT_IMAGEINFO/MSG_GET for both types of sane backends.
Since some backends have only one option "resolution" for both X and Y resolution, while others provide separate options for "x-resolution" and "y-resolution", there are a lot of possible combinations.
Some backends do not allow read access to to their options once scanning has started. This had the consequene that for these backends, DG_IMAGE/DAT_IMAGEINFO/MSG_GET specified a resolution of -1. For that reason the current X/Y Resolution is now cached in activeDS before starting the scan.
One backend that uses TYPE_FIXED is the SANE "test" backend. When setting a resolution, the test backend rounds to the nearest integer, so 300.4 DPI get 300.0 DPI and 300.6 DPI git 301 DPI.
The test backend is not the only backend that stores resolution as TYPE_FIXED.
This MR also contains code to display the resolution in DPI and the paper size calculated by pixel width/height and resolution in the progress dialog. If LOCALE_IMEASURE says that the locale applies the metric system, sizes are displayed in mm, otherwise (USA) sizes are displayed in inch.