Instead of introducing a global variable, use the already existing
saved android_app pointer in lo-bootstrap.c, and just add a function
to retrieve it from there. Store it in the AndroidSalInstance.
Reanme osl/detail/android.h back to android_native_app_glue.h, which
is the name of that file in NDK/sources. "android.h" sounded to me too
grand, as if it was some universal Android header. But if we do start
to modify the android_native_app_glue stuff heavily, then it indeed
makes sense to call it something else. Until then, revert also some
whitespace changes to android_native_app_glue.c for it to be as close
as possible to the "upstream" one in the NDK, for clarity.
Having SvFileStream call the file opening etc functions here, instead
of calling open() directly itself, means we won't have to duplicate
the Android .apk hooks there, too.
