Extend jni methods and enable Beginning-of-Sentence.

java/src/com/android/inputmethod/latin/BinaryDictionary.java

...android/inputmethod/latin/ExpandableBinaryDictionary.java

java/src/com/android/inputmethod/latin/PrevWordsInfo.java

.../com/android/inputmethod/latin/makedict/WordProperty.java

...ve/jni/com_android_inputmethod_latin_BinaryDictionary.cpp

...ary/structure/pt_common/dynamic_pt_gc_event_listeners.cpp

...roid/inputmethod/latin/BinaryDictionaryDecayingTests.java

.../com/android/inputmethod/latin/BinaryDictionaryTests.java

...m/android/inputmethod/latin/makedict/Ver4DictEncoder.java