Add warning flags to the DEBUG_CFLAGS too.

This fixes several bugs/incompatibilities in spudvb decoder.
You can find various test samples at http://hftom.free.fr/video_samples/

--HG--
extra : transplant_source : %CD%CE%3A%3F%B6%8BN%FD2%5D%DB%9A%AB%AF%C2%E1%2B%1A%B1%23

With this change a lot of variables now result unused, as before they
were only assigned after declaration.

--HG--
extra : transplant_source : S%D1%AF%8B%F9%C12%16%B2%F7%F0%A6zpA%5C%C7%12%AE%E8

The xine_xmalloc() function is going to be deprecated, as its
behaviour is rarely needed as such, and it's thus misused.

With this, almost all uses of xine_xmalloc() with static size (for
instance the value returned by sizeof()) or with a size that is
guaranteed not to be zero (like strlen()+1) are replaced with calls to
either calloc(1, ...) or malloc().

malloc() is used whenever the allocated memory is going to be
immediately overwritten, while calloc() is used in every other case,
as it sets the whole memory area to zero.

--HG--
extra : transplant_source : %8F%98%EC%02%1E%83%F0s%06X%83C%205Y%80%B12%CC%E1

- Allow visible region updates.
- Resize OSD at drawing time.

--HG--
extra : transplant_source : %17%ECZ%D0j%2C%BC%06%7CO%3A%F0%C7u%A3%86%DE%8Bb%D3

--HG--
extra : transplant_source : %E0%D0%C5%8B%BEU%DD%24%5D7%1F%ADV%AD%EB%23%CBU%80%EB