Modernize "C" includes in search.

This is one of those little chores in managing a long-lived C++
project: standard C headers like stdio.h and math.h now have their own
place in the C++ standard as resp. cstdio, cmath, and so on.  In this
branch the #include names are updated for the search/ subdirectory; more
branches to follow.

C++11 adds cstdint, but to support compilation with the previous
standard, that change is left for later.

search/applied.hh

@@ -5,7 +5,7 @@
 #include "search/header.hh"
 #include "util/pool.hh"
 
-#include <math.h>
+#include <cmath>
 
 namespace search {
 

search/nbest.cc

@@ -6,9 +6,8 @@
 #include <algorithm>
 #include <functional>
 #include <queue>
-
-#include <assert.h>
-#include <math.h>
+#include <cassert>
+#include <cmath>
 
 namespace search {
 

search/nbest.hh

@@ -10,8 +10,7 @@
 #include <cstddef>
 #include <queue>
 #include <vector>
-
-#include <assert.h>
+#include <cassert>
 
 namespace search {
 

search/rule.cc

@@ -5,7 +5,7 @@
 
 #include <ostream>
 
-#include <math.h>
+#include <cmath>
 
 namespace search {
 

search/vertex.cc

@@ -6,8 +6,7 @@
 
 #include <algorithm>
 #include <functional>
-
-#include <assert.h>
+#include <cassert>
 
 namespace search {
 

search/vertex.hh

@@ -8,8 +8,7 @@
 
 #include <queue>
 #include <vector>
-
-#include <math.h>
+#include <cmath>
 #include <stdint.h>
 
 namespace search {