Renamed PAGE defines to MPAGE so as not to conflict with the android ndk

Fixes build with Android NDK r9 for ARM and x86 with NDK_TOOLCHAIN_VERSION=clang. GCC 4.6 and 4.8 still fail with internal compiler errors, and MIPS still doesn't link, even with clang. Still, I don't think the various PAGE defines that are conflicting will be going away in the next NDK version, so it's best to fix this now