[AD] Update on `const'

[Laurence Withers <lwithers@xxxxxxxxxx>]

Hi,

Since we implemented `const'-correctness in the library, I have learnt
several more things about `const', and gained some experience using it
(both in my own applications and elsewhere). I have a couple of points
which may be of interest:

 - `const' is C89. This means that probably every compiler we use 
   accepts it, so we can do away with the ugly AL_CONST and just
   use plain const. If this does prove to be a problem anywhere, we can 
   use preprocessor trickery to solve it.

 - Several functions have incorrect semantics, taking a const pointer
   but returning a mutable one. An example of this is `get_filename'. I
   suppose the idea behind it is that the function doesn't alter the
   string, so it is passed as `const', but the user might want to alter
   it afterwards, so it is returned as mutable. This is not really 
   valid; in actual fact, in situations like this, we should have two
   functions:

char* get_filename(char* path);
const char* get_filename_const(const char* path);

   We have to treat `char*' and `const char*' as separate types.

Ideally, I would like to change these two things, but I am unsure of
where we are heading at the moment (new API, etc). What do you think?

Bye for now,
-- 
Laurence Withers, lwithers@xxxxxxxxxx
                http://www.lwithers.demon.co.uk/

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