Use int32 for parameter block sizes.

CostFunction now uses int32 instead of int16
to store the size of its parameter blocks.

This is an API breaking change.

Change-Id: I032ea583bc7ea4b3009be25d23a3be143749c73e
diff --git a/internal/ceres/problem_impl.cc b/internal/ceres/problem_impl.cc
index 09eed9e..37cd351 100644
--- a/internal/ceres/problem_impl.cc
+++ b/internal/ceres/problem_impl.cc
@@ -224,7 +224,7 @@
            cost_function->parameter_block_sizes().size());
 
   // Check the sizes match.
-  const vector<int16>& parameter_block_sizes =
+  const vector<int32>& parameter_block_sizes =
       cost_function->parameter_block_sizes();
 
   if (!options_.disable_all_safety_checks) {