[RFC] spatch to drop check after alloc/lalloc/xmalloc

Sample of what can done with [coccinelle](http://coccinelle.lip6.fr/) for helping resolving tickets like #488 . This patch built by:
````
spatch --in-place --sp-file allocs.cocci src/*.c
````
When contents of `allocs.cocci`:
````patch
@@ identifier p; @@
  p =
(
  alloc(...)
|
  lalloc(...)
|
  xmalloc(...)
)
  ;
- if (p == NULL) { ... }
````