CLEANUP: remove unneeded casts

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.