CLEANUP: remove unneeded casts

In C89, "void *" is automatically promoted to any pointer type. Casting
the result of malloc/calloc to the type of the LHS variable is therefore
unneeded.

Most of this patch was built using this Coccinelle patch:

@@
type T;
@@

- (T *)
  (\(lua_touserdata\|malloc\|calloc\|SSL_get_app_data\|hlua_checkudata\|lua_newuserdata\)(...))

@@
type T;
T *x;
void *data;
@@

  x =
- (T *)
  data

@@
type T;
T *x;
T *data;
@@

  x =
- (T *)
  data

Unfortunately, either Coccinelle or I is too limited to detect situation
where a complex RHS expression is of type "void *" and therefore casting
is not needed. Those cases were manually examined and corrected.

src/ev_kqueue.c

@@ -155,7 +155,7 @@ REGPRM1 static int _do_init(struct poller *p)
 		goto fail_fd;
 
 	/* we can have up to two events per fd (*/
-	kev = (struct kevent*)calloc(1, sizeof(struct kevent) * 2 * global.maxsock);
+	kev = calloc(1, sizeof(struct kevent) * 2 * global.maxsock);
 	if (kev == NULL)
 		goto fail_kev;