Codechange: Use override specifer for overriding member declarations

This is a C++11 feature that allows the compiler to check that a virtual
member declaration overrides a base-class member with the same signature.

Also src/blitter/32bpp_anim_sse4.hpp +38 is no longer erroneously marked
as virtual despite being a template.

(svn r17214) -Add [NoAI]: GetAPIVersion() as optional function in info.nut. Return "0.7" to get an api compatible (as much as possible) with the 0.7 api or "0.8" to get the latest api.
-Change [NoAI]: move all deprecated functions to a separate squirrel script that is only loaded if an AI requests an old API version.

(svn r16502) -Fix [FS#2935]: when an AI was suspended while in a function called (indirectly) via call/acall/pcall OpenTTD crashed. Fix this by disallowing AIs to be suspended while called via call/acall/pcall.
IMPORTANT FOR AI WRITERS: AIs can no longer call any DoCommand functions (change anything, build vehicles, etc.) in a function called (indirectly) via call/acall/pcall. Where possible, please rewrite your code so it doesn't use call/acall/pcall

(svn r15045) -Add [NoAI API CHANGE]: in info.nut you can now have (optional) a CanLoadFromVersion(version), which should return true/false, to indicate if you can load a savegame made with your AI of version 'version'
-Add [NoAI API CHANGE]: in main.nut the Load() function now should be Load(version, data), where 'version' is the version of your AI which made the savegame
-Codechange [NoAI]: various of function renames to make things more sane
-Add [NoAI]: push the 'version' of the AI through various of layers
-Codechange [NoAI]: various of code cleanups
-Add [NoAI]: store the version of the AI in the savegame too

(svn r15027) -Merge: tomatos and bananas left to be, here is NoAI for all to see.
NoAI is an API (a framework) to build your own AIs in. See:
http://wiki.openttd.org/wiki/index.php/AI:Main_Page
With many thanks to:
- glx and Rubidium for their syncing, feedback and hard work
- Yexo for his feedback, patches, and AIs which tested the system very deep
- Morloth for his feedback and patches
- TJIP for hosting a challenge which kept NoAI on track
- All AI authors for testing our AI API, and all other people who helped in one way or another
-Remove: all old AIs and their cheats/hacks