Fix file name typo, thanks Sam Clegg!

--HG--
rename : src/filesystem/nacl/SDL_sysfilesytem.c => src/filesystem/nacl/SDL_sysfilesystem.c
Make autoconf-based build quiet by default.

Add V=1 to the make command line will show the full commands but by default
we just show the tool-type and the output file.  This is generally much easier
on the eye and makes warnings and errors more clearly visible.
Initialize nacl_io, removes SDL_NaClMount/Umount

It's just easier to use nacl_io's mount/umount directly.
Ooops, code that resists erasure, I've seen that in a movie.
Fix compiler warnings in Native Client and Linux builds.
Fix another NaCl warning