[FIXED] #11572 Filter Legend By Map Content doesn't maintain point displacement legend

The fix from https://github.com/qgis/QGIS/pull/1673 has to be enhance to have
 something more generic.

This fix add methods to QgsPointDisplacementRenderer:
* capabilities
* symbolForFeature
* originalSymbolForFeature
* symbolsForFeature
* originalSymbolsForFeature
* willRenderFeature
prepare-commit.sh: fix script directory detection
fixes r.watershed parameter description for GRASS 6.4
indentation update and typo fixes
Merge pull request #1687 from gioman/master

fixes r.watershed parameter description for GRASS 6.4
pull_ts.sh: verify lrelease is available
avoid use of QIcon in data items in threads
Initialize some uninitialized variables
Add .travis.yml for automated testing
[unit tests] Add multirenderchecker

The multirenderchecker allows to have several images, each with its own set of
anomalies distributed in several subdirectories.
With the help of multiple reference images, it is possible to apply a color
tolerance to each of these
Compositionchecker: Default color tolerance of 1
[unit tests] Fix blend modes test

 * Switched to QgsMultiRenderChecker and added control images for precise
 * Add a minimal color tolerance for slight render inconsistencies
Fix inverted polygon renderer test
Fix PalLabelingComposer test

Switch to QgsMultiRenderChecker and add control images for Ubuntu precise where
required.
[unit tests] Make qgis_rendererstest pass

Replace control image
Fix shapeburst test

Move to multirenderchecker
Cleanup atlas composition tests

 * Don't try to cache on 0-sized image
 * Use qDebug instead of qWarning
Use a non-transparent background for composition checker

Fix composerhtml tests on precise
Switch to RGB32 images for composition checker
Switch QgsCompositionChecker to MultiRenderChecker