Metadata viewer: indicate that the focal length is given in milimeters
Metadata viewer: don't display invalid/unusable "focus distance" values
color picker: backtransform picker coordinates; fixes #9482

coordinates of local color picker need to be transformed back from the preview
image to the module in focus, else we pick completely bogus spots if distorting
modules are in action.
color picker: better account for invalid local color picker data in several places

if the local color picker is positioned outside the module's image area it can not
deliver valid data. take appropriate action in this case (depends on where we use
the color picker).
blending: add option to toggle polarity of drawn mask

this is needed to effectively extend a parametric mask by including or
excluding specific parts of an image.

to include parts: switch combobox combine to "inclusive" and make sure
polarities of drawn mask and parametric mask channels are set to negative.

to exclude parts: switch combobox combine to "exclusive" and make sure
polarities of drawn mask and parametric mask channels are set to positive.

use "inclusive & inverted" or "exclusive & inverted" to get an inverted mask
if needed.

the "toggle polarity" button (circle with black&white) can be used to quickly
toggle between inclusive and exclusive mode.
Add two more guides to c&r, perspective + metering
fixes bug #9487
Fix a crash when live view is not supported ...

... and live view is switched on and off again
graduatednd: fix (marginal) bug in distance calculation
Merge branch 'master' of ssh://github.com/darktable-org/darktable
fix a few memleaks
Update Polish translation
cache: make stats work on legacy compiler + arch.
Merge pull request #251 from jktjkt/metadata-viewer-tweaks

Metadata viewer tweaks
Merge pull request #256 from adsr303/plpo

Update Polish translation
Button to select between to split view or overlay
Create snapshots table and add a snapshot number column to images table
Several snapshots history and name saving

 + Write snapshot's history to xmp (TO BE FIXED)
 + Write snapshot's history to db
 + Write snapshot's name to db
TODO: we also need to read snapshots info from xmp file
Small modification in colums name in snapshots table