Fix iOS warnings about implicit conversion precision by changing double literals to float ones

Conflicts:
	modules/contrib/include/opencv2/contrib/retina.hpp

modules/core/include/opencv2/core/affine.hpp

@@ -253,7 +253,7 @@ void cv::Affine3<T>::rotation(const Vec3& _rvec)
         double c = std::cos(theta);
         double s = std::sin(theta);
         double c1 = 1. - c;
-        double itheta = theta ? 1./theta : 0.;
+        double itheta = (theta != 0) ? 1./theta : 0.;
 
         rx *= itheta; ry *= itheta; rz *= itheta;
 

modules/flann/include/opencv2/flann/miniflann.hpp

@@ -89,13 +89,13 @@ struct CV_EXPORTS LinearIndexParams : public IndexParams
 struct CV_EXPORTS CompositeIndexParams : public IndexParams
 {
     CompositeIndexParams(int trees = 4, int branching = 32, int iterations = 11,
-                         cvflann::flann_centers_init_t centers_init = cvflann::FLANN_CENTERS_RANDOM, float cb_index = 0.2 );
+                         cvflann::flann_centers_init_t centers_init = cvflann::FLANN_CENTERS_RANDOM, float cb_index = 0.2f );
 };
 
 struct CV_EXPORTS AutotunedIndexParams : public IndexParams
 {
-    AutotunedIndexParams(float target_precision = 0.8, float build_weight = 0.01,
+    AutotunedIndexParams(float target_precision = 0.8f, float build_weight = 0.01f,
-                         float memory_weight = 0, float sample_fraction = 0.1);
+                         float memory_weight = 0, float sample_fraction = 0.1f);
 };
 
 struct CV_EXPORTS HierarchicalClusteringIndexParams : public IndexParams
@@ -107,7 +107,7 @@ struct CV_EXPORTS HierarchicalClusteringIndexParams : public IndexParams
 struct CV_EXPORTS KMeansIndexParams : public IndexParams
 {
     KMeansIndexParams(int branching = 32, int iterations = 11,
-                      cvflann::flann_centers_init_t centers_init = cvflann::FLANN_CENTERS_RANDOM, float cb_index = 0.2 );
+                      cvflann::flann_centers_init_t centers_init = cvflann::FLANN_CENTERS_RANDOM, float cb_index = 0.2f );
 };
 
 struct CV_EXPORTS LshIndexParams : public IndexParams