(svn r1861) Constify Get(Non)Sprite()

(svn r1860) The sprite header endianness issue was solved in r1855

(svn r1859) Miscellaneous style changes

(svn r1858) Let ReadSprite() handle the subtleties of loading a sprite, not its caller

(svn r1857) Rewrite parts of the sprite heap. It's functionally equivalent but should be easier to read and maintain.

(svn r1856) Make GfxInitSpriteMem() static, because it's only used withing spritecache.c

(svn r1855) Handle endianness of sprite headers when loading a sprite, not everytime when accessing it

(svn r1854) Split GetSpritePtr() into GetSprite() for regular sprites (returning a Sprite*) and GetNonSprite() for "sprites" of type 0xFF (returning byte*)

(svn r1853) Move spritecache function declarations into a header of their own and use SpriteID as parameter type where appropriate

(svn r1852) Start cleaning up sprite handling:
- Complement the sprite header struct with a variable sized array for the sprite data and rename it to Sprite.
- Use the correct type Sprite* instead of casting all the time (this causes some "assignment from incompatible pointer type" warnings, nothing serious, will be resolved soon)

(svn r1851) - Language: added Frisian translation (no strings have been translated yet)

(svn r1850) Change the last consumers of str_buffr so they use local static buffers now and remove the global array str_buffr.

(svn r1849) Use the cheat entry enum for CheatEntry.type and remove unused enum values

(svn r1848) Remove the obscure feature of initialising the edit box with the contents of str_buffr - it was unused anyway.
Remove it from the chat box too, which inherited it via copy&paste.