[issue26855] add platform.android_ver() for android

[Chi Hsuan Yen]

Chi Hsuan Yen added the comment:

> Also how can we be sure that the '/system/build.prop' file may be guaranteed to exist on all android devices ?

This path is hard-coded in BioniC [1]. Though I can't find a document/relevant source codes to guarantee 'ro.build.version.release' and 'ro.build.version.sdk' is always in /system/build.prop

And the format of build.prop is not exactly INI. It supports 'import' clauses. See [2] and load_properties() function in [3]

Other options include calling `getprop` via subprocess or using C level function __system_property_get(). The first approach should always work. It's just somewhat tricky on Android 4.1 [4]. For the second option, a bad news is that it's a private API and was just removed from the latest NDK. Chromium has a workaround for that [5] and CPython may use similar approaches.

[1] https://android.googlesource.com/platform/bionic/+/master/libc/include/sys/_system_properties.h
[2] http://forum.xda-developers.com/android/general/explanation-build-prop-values-t3069341
[3] https://android.googlesource.com/platform/system/core/+/master/init/property_service.cpp
[4] https://github.com/rave-engine/python3-android/pull/10#issuecomment-159151445
[5] https://groups.google.com/a/chromium.org/forum/#!topic/chromium-reviews/keQP6L9aVyU

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nosy: +Chi Hsuan Yen

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