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This also prepares for a major shift in the way files are stored under
development/ndk. Essentially, after this patch, you can have:

development/ndk/android-N/arch-$ABI/
  ==> contains only files relevant to API level 'N' that are not
      already part of API level 'N-1', 'N-2', etc...

development/ndk/android-N/samples/
  ==> contains samples that depend on features of a given API level 'N'.

The idea is to be able to work on API level 'N+1' by adding a single
directory under development/ndk. This is useful when branching between
several platform release branches. And it makes platform additions
trivial to examine and check.

+ build/tools/build-platforms.sh: group all files under development/ndk
  under $NDK/platforms and $NDK/samples, grouping everything together

+ build/tools/dev-cleanup.sh: get rid of all intermediate files,
  including $NDK/platforms and $NDK/samples

+ update make-release.h to deal with the new hotness.

Change-Id: I1c26052b862af4c319b9c0a5757c585929650562