[svn r18] * Initial support for switch statements - No string switches yet.

* Moved Statement::toIR definitions into gen/statements.c - toir.c is still too big.
* Removed some BB bloat with ScopeStatements.

test/switch1.d

@@ -0,0 +1,15 @@
+module switch1;
+
+void main()
+{
+    int i = 2;
+    int r;
+    switch (i)
+    {
+    case 1: r+=1; break;
+    case 2: r-=2;
+    case 3: r=3; break;
+    default: r=-1;
+    }
+    assert(r == 3);
+}