DebugTools: more convenience CompareImage constructors.

I need to pass both the importer and converter managers but don't need
any thresholds.

src/Magnum/DebugTools/CompareImage.h

@@ -449,6 +449,15 @@ class CompareImageFile {
          */
         explicit CompareImageFile(PluginManager::Manager<Trade::AbstractImporter>& importerManager, PluginManager::Manager<Trade::AbstractImageConverter>& converterManager, Float maxThreshold, Float meanThreshold): _c{&importerManager, &converterManager, maxThreshold, meanThreshold} {}
 
+        /**
+         * @brief Construct with an explicit importer and converter plugin manager instance and implicit thresholds
+         * @m_since_latest
+         *
+         * Equivalent to calling @ref CompareImageFile(PluginManager::Manager<Trade::AbstractImporter>&, PluginManager::Manager<Trade::AbstractImageConverter>&, Float, Float)
+         * with zero values.
+         */
+        explicit CompareImageFile(PluginManager::Manager<Trade::AbstractImporter>& importerManager, PluginManager::Manager<Trade::AbstractImageConverter>& imageConverterManager): _c{&importerManager, &imageConverterManager, 0.0f, 0.0f} {}
+
         /**
          * @brief Construct with implicit thresholds
          *
@@ -512,6 +521,15 @@ class CompareImageToFile {
          */
         explicit CompareImageToFile(PluginManager::Manager<Trade::AbstractImporter>& importerManager, PluginManager::Manager<Trade::AbstractImageConverter>& imageConverterManager, Float maxThreshold, Float meanThreshold): _c{&importerManager, &imageConverterManager, maxThreshold, meanThreshold} {}
 
+        /**
+         * @brief Construct with an explicit importer and converter plugin manager instance and implicit thresholds
+         * @m_since_latest
+         *
+         * Equivalent to calling @ref CompareImageToFile(PluginManager::Manager<Trade::AbstractImporter>&, PluginManager::Manager<Trade::AbstractImageConverter>&, Float, Float)
+         * with zero values.
+         */
+        explicit CompareImageToFile(PluginManager::Manager<Trade::AbstractImporter>& importerManager, PluginManager::Manager<Trade::AbstractImageConverter>& imageConverterManager): _c{&importerManager, &imageConverterManager, 0.0f, 0.0f} {}
+
         /**
          * @brief Implicit constructor
          *