Fix warnings on gcc

gtsam/sfm/DsfTrackGenerator.cpp

@@ -39,7 +39,8 @@ static DSFMapIndexPair generateDSF(const MatchIndicesMap& matches) {
     // Image pair is (i1,i2).
     size_t i1 = pair_indices.first;
     size_t i2 = pair_indices.second;
-    for (size_t k = 0; k < corr_indices.rows(); k++) {
+    size_t m = static_cast<size_t>(corr_indices.rows());
+    for (size_t k = 0; k < m; k++) {
       // Measurement indices are found in a single matrix row, as (k1,k2).
       size_t k1 = corr_indices(k, 0), k2 = corr_indices(k, 1);
       // Unique key for DSF is (i,k), representing keypoint index in an image.

gtsam/sfm/ShonanAveraging.h

@@ -366,7 +366,7 @@ class GTSAM_EXPORT ShonanAveraging {
   template <class T>
   static Values LiftTo(size_t p, const Values &values) {
     Values result;
-    for (const auto it : values.extract<T>()) {
+    for (const auto& it : values.extract<T>()) {
       result.insert(it.first, SOn::Lift(p, it.second.matrix()));
     }
     return result;