* Android-21 introduced an API for symlinking.
* Android-19 has an API which can be used via reflection.
* Earlier versions use Runtime.exec('/system/bin/ln')
This also extends the SanitizedFile stuff so that the android < 19 can
safely use Runtime.exec() with less fear of command injection vulnerabilities.
Finally, some tests for the SanitizedFile and symlink stuff was added.
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