[PATCH 0/2] Adding some 'const' qualifiers

[Christophe]

Hello,

I am proposing 2 patches in order to improve a little bit things
for the compiler. The first patch changes only internal stuff, so
there's no risk.

The second patch however modifies the external API, but I believe
there is no risk because it does not change any behaviour nor
binary compatibility with previous releases, and will not introduce
new warning on user side at compilation.

This does not fix any libXpm compilation warning, because those
would require an API change that might break compatibility.

Best regards,
Christophe.