CMake: Replace "else(condition)" with "else()", etc.

Bumped required CMake version to 2.8.

Thanks to the SDL/Emscripten porting team for this cleanup.

--HG--
extra : rebase_source : 2b9bf6b045956f4607d2911265a136359a3fbdcb
Initial merge of Emscripten port!

With this commit, you can compile SDL2 with Emscripten
( http://emscripten.org/ ), and make your SDL-based C/C++ program
into a web app.

This port was due to the efforts of several people, including: Charlie Birks,
Sathyanarayanan Gunasekaran, Jukka Jylänki, Alon Zakai, Edward Rudd,
Bruce Mitchener, and Martin Gerhardy. (Thanks, everyone!)

--HG--
extra : rebase_source : 97af74c8a5121e926ebe89f123536b5dd6681695
CMake: Minor cleanup up on the new SDL_*_ENABLED_BY_DEFAULT vars.

--HG--
extra : rebase_source : af065b92bfba14673c2c76606339fe6a1e449e86