Fix clang warnings in core/jni.

There are a few bugs in here too (mostly people expecting + to
concatenate C strings) :(

Change-Id: I0a243c05c4ea8b56e84896f37814d0fbea4c39d5
Add appropriate casts for char16_t.

C++11 defines a real char16_t, which is not implicitly convertible to
uint16_t (and by extension jchar). Add casts as needed.

Bug: 18300613
Change-Id: I00752002ef2e938bdb57f70947e8fd53ec103293
Merge "Add appropriate casts for char16_t."
Merge "Fix clang warnings in core/jni."
Fix format strings mismatching the parameters passed to them

Change-Id: Ia0d33aec9edadac60508fb422e0821e6d8f28afa
Signed-off-by: Bernhard Rosenkränzer <Bernhard.Rosenkranzer@linaro.org>
Merge "Fix format strings mismatching the parameters passed to them"