Looks for correct ndk-build command.

If the build-native.sh script points to a different ndk-build
executable, it uses it.

If not, compile.sh looks for a build-native.sh in the $PATH and, if
present, correct the possible erroneous path in build-native (just to
avoid silly edits in that file), and compiles with it.
Debug does not wipe data.

Minor fixes in the other files.
Debug does not wipe data.

Minor fixes in the other files.
We need API 15 installed.
leap_android is now bitmask_android
Each step refers to the previous one.

Instead of repeating preconditions, or composing sentences which take some things as obvious (e.g., the android client can be compiled using eclipse, but that does not mean that the run.sh script will work), I refer each step to the previous one.