This replaces the custom LittleEndianDataInputStream with
guava's implementation. To do this, I had to fix ExtDataInput
to better handle the case where skipBytes doesn't skip all the
bytes (the tests failed without this, and succeed with it). This
appears to be the main difference between the two implementations.
Guava's implementation is preferred because it is already a
dependency and because its license is clearer (the previous
implementation had a vague "public domain" comment in the thread
which may not be legally sufficient).
Fixes#1166
