Have configure check for SDL2
Initial attempt
Necessary slash
Make win32 save dir relative to steam common dir
Use relative save directory if STEAM defined

The linux one appears to work. The others will be tested shortly.
Fix windows local GetSavePath

Appears to work correctly on windows with these changes.
Make linux local save dir relative to exe

Before it was relative to cwd. Also did some refactoring.
Locate save folder based on AppInstallDir

Also, some patching up of the existing save folder functions.
This is all only tested on Linux as of this commit.
Update install w/ aclocal, remove unneeded exports
Merge branch 'SteamApi' into SteamSavedir2
Fix OSX local saves dir, and make local saves dir a compile-time option
Merge Steam Save Dir support