Change type of totalBits and curPos
Change type of totalBits and curPos

The int type is too small for larger datasets.  It seems
that has already caused us to under-estimate our space usage on
e.g. the 5k E. coli genome dataset.  These changes use size_t for
these types eliminating this problem.
COMBINE-lab/rainbowfish,COMBINE-lab/rainbowfish