Update Box2D to 2.4.2 for LÖVE 12 release

[tpimh]

v2.4.2 is the final release of version 2 of Box2D, and mostly a bugfix release. I don't suggest switching to a new major version, but such small update should probably be good.

[tpimh]

Let's see what's different between Box2D 2.4.1 in LÖVE and upstream 2.4.1:

--- box2d-2.4.1/box2d/b2_common.h
+++ love2d/box2d/b2_common.h
@@ -34,7 +34,8 @@
 #endif
 
 #define B2_NOT_USED(x) ((void)(x))
-#define b2Assert(A) assert(A)
+void loveAssert(bool test, const char* teststr);
+#define b2Assert(A) loveAssert((A), #A)
 
 #define	b2_maxFloat		FLT_MAX
 #define	b2_epsilon		FLT_EPSILON

--- box2d-2.4.1/box2d/b2_math.h
+++ love2d/box2d/b2_math.h
@@ -24,6 +24,7 @@
 #define B2_MATH_H
 
 #include <math.h>
+#include <cmath>
 
 #include "b2_api.h"
 #include "b2_settings.h"
@@ -31,7 +32,7 @@
 /// This function is used to ensure that a floating point number is not a NaN or infinity.
 inline bool b2IsValid(float x)
 {
-	return isfinite(x);
+	return std::isfinite(x);
 }
 
 #define	b2Sqrt(x)	sqrtf(x)

--- box2d-2.4.1/box2d/Box2D.h
+++ love2d/box2d/Box2D.h
@@ -43,6 +43,7 @@
 #include "b2_time_step.h"
 #include "b2_world.h"
 #include "b2_world_callbacks.h"
+#include "b2_distance.h"
 
 #include "b2_distance_joint.h"
 #include "b2_friction_joint.h"

--- box2d-2.4.1/box2d/common/b2_settings.cpp
+++ love2d/box2d/common/b2_settings.cpp
@@ -27,6 +27,8 @@
 #include <stdarg.h>
 #include <stdlib.h>
 
+#include "common/Exception.h"
+
 b2Version b2_version = {2, 4, 0};
 
 // Memory allocators. Modify these to use your own allocator.
@@ -46,6 +48,12 @@
 	vprintf(string, args);
 }
 
+void loveAssert(bool test, const char* teststr)
+{
+	if (!test)
+		throw love::Exception("Box2D assertion failed: %s", teststr);
+}
+
 FILE* b2_dumpFile = nullptr;
 
 void b2OpenDump(const char* fileName)

--- box2d-2.4.1/box2d/dynamics/b2_island.cpp
+++ love2d/box2d/dynamics/b2_island.cpp
@@ -30,7 +30,7 @@
 #include "box2d/b2_world.h"
 
 #include "b2_island.h"
-#include "dynamics/b2_contact_solver.h"
+#include "b2_contact_solver.h"
 

Not much actually. Let's see what changed in the new version: erincatto/box2d@v2.4.1...v2.4.2

Also not much. Most notably: final removal of RopeJoint erincatto/box2d@7e871b8 (was already mostly removed in 2.4.1: erincatto/box2d@8733e60) and weird fix for erincatto/box2d#681 (code fixed to match documentation instead of fixing the documentation to match the code). I think I will create a WIP PR with these changes now.