Add projectiles through obstacle test

The bug where projectiles cannot go through obstacles has come up at
least 2 times. Let's get a test for this so we can know before it
happens.

tests/projectile_test.cpp

@@ -0,0 +1,60 @@
+#include "catch/catch.hpp"
+
+#include "avatar.h"
+#include "ballistics.h"
+#include "dispersion.h"
+#include "game.h"
+#include "itype.h"
+#include "map.h"
+#include "map_helpers.h"
+#include "projectile.h"
+
+static tripoint projectile_end_point( const std::vector<tripoint> &range, const item &gun,
+                                      int speed, int proj_range )
+{
+    projectile test_proj;
+    test_proj.speed = speed;
+    test_proj.range = proj_range;
+    test_proj.impact = gun.gun_damage();
+    test_proj.proj_effects = gun.ammo_effects();
+    test_proj.critical_multiplier = gun.ammo_data()->ammo->critical_multiplier;
+
+    dealt_projectile_attack attack;
+
+    attack = projectile_attack( test_proj, range[0], range[2], dispersion_sources(), &g->u, nullptr );
+
+    return attack.end_point;
+}
+
+TEST_CASE( "projectiles_through_obstacles", "[projectile]" )
+{
+    clear_map();
+
+    // Move the player out of the way of the test area
+    g->u.setpos( { 2, 2, 0 } );
+
+    // Ensure that a projectile fired from a gun can pass through a chain link fence
+    // First, set up a test area - three tiles in a row
+    // One on either side clear, with a chainlink fence in the middle
+    std::vector<tripoint> range = { tripoint_zero, tripoint_east, tripoint( 2, 0, 0 ) };
+    for( const tripoint &pt : range ) {
+        REQUIRE( g->m.inbounds( pt ) );
+        g->m.ter_set( pt, ter_id( "t_dirt" ) );
+        g->m.furn_set( pt, furn_id( "f_null" ) );
+        REQUIRE_FALSE( g->critter_at( pt ) );
+        REQUIRE( g->m.is_transparent( pt ) );
+    }
+
+    // Set an obstacle in the way, a chain fence
+    g->m.ter_set( range[1], ter_id( "t_chainfence" ) );
+
+    // Create a gun to fire a projectile from
+    item gun( itype_id( "m1a" ) );
+    gun.ammo_set( "308", 5 );
+
+    // Check that a bullet with the correct amount of speed can through obstacles
+    CHECK( projectile_end_point( range, gun, 1000, 3 ) == range[2] );
+
+    // But that a bullet without the correct amount cannot
+    CHECK( projectile_end_point( range, gun, 10, 3 ) == range[0] );
+}