Delta representations store a checksum for the fulltext, but do not currently
use it when undeltifying. In some cases (subrange reads), we cannot use the
checksum anyway; but when we're reading the whole file, we can. Fix so that
in the latter case, we do check against it.
For now, in reps-strings.c, this probably means that rep_read_range() should
accumulate a checksum in the window_baton, and check it when done. This will
at least take care of verification on files that are read in one call to
rep_read_range(), which is better than nothing.
Major SVN-414 finish deltification
