[AD] Regarding backwards compatibility of 4.1.x and 4.x where x >= 2

[Grzegorz Adam Hankiewicz <gradha@xxxxxxxxxx>]

Now the webpage features:

 "We intend to maintain backwards compatibility with the current
 Allegro API (except for some obscure features). Most of the time,
 this will be done using a compatibility layer -- the old API will
 be layered on top of the new API."

However, I've just finished reading "Game programming all in one
2nd edition" by Jonathan S. Harbour.  At the end of Appendix E you
can find the text:

 "...but based on my experience with as recent a version as 4.1.12,
 which is not compatible with 4.0.3... I am only officially
 supporting 4.0.3..."

Which kind of contradicts the proclaimed intention, unless the non
compatibility issue is with regards to some obscure features.

Should the future compatibility layer be implemented now on top
of the current WIP and make sure that WIPS compile cleanly with
software using 4.0.3?  Doesn't this make useless the deprecation
warnings of the current WIPs? AFAICS "deprecated" tries to bring
attention to the developer that a symbol is going to disappear, but
if the developer only has to add a new include to the source code, I
would prefer if those warnings forecasting the apocalypse went away.