The BacktracePtrace::Read function crashes if the number of bytes to
read is less than the number of bytes needed to align the read to
a word_t boundary.
Fix this and add a test for this case.
Change-Id: I50808849ece44928f65dba1d25309e3885c829a2
(cherry picked from commit 944f417ccb)
The object hierarchy was confusing and convoluted. This removes
a lot of unnecessary code, and consolidates the BacktraceCurrent
and BacktraceThread code into BacktraceCurrent.
Change-Id: I01c8407d493712a48169df49dd3ff46db4a7c3ae