Searching the installed man pages for SDL functions fails, e.g.
  man -k SDL_ |grep Video
After investigating this I found that "makewhatis", the tool that generates
the "whatis" database, reads the SDL_* man pages, but doesn't produce
entries in the "whatis" database for the SDL_* man pages.
After some more debugging I found the reason is a missing space.
After editing SDL_Init.3(.gz) and replacing
   SDL_Init\- Initializes SDL
with
   SDL_Init \- Initializes SDL
everything works fine.
After running "makewhatis" I can successfully do a
   man -k SDL_
and SDL_Init is listed in the output.

--HG--
branch : SDL-1.2
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/branches/SDL-1.2%402660

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%40182

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%4056

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%401