Don't try to set thread scope and scheduling policy on android

These APIs aren't implemented on android.
add memalign unit test
specific slice mode in encoder test
Merge pull request #467 from sijchen/add_more_slice_mode_test

Specific slice mode in encoder test
Merge pull request #466 from sijchen/add_memalign_test

Add memalign unit test
Merge pull request #458 from mstorsjo/android-threading

Don't try to set thread scope and scheduling policy on android