The last line of a non newline-terminated file would mix with the first line of
the next file in multiple-file listings before this patch.
Possible compatibility issue: no longer possible to tell from the annotate
output if the file is terminated by new line or not.
splitblock() was added to handle blocks returned by bdiff.blocks() which differ
only by blank lines but are not made only of blank lines. I do not know exactly
how it could happen but mdiff.blocks() threshold behaviour makes me think it
can if those blocks are made of very popular lines mixed with popular blank
lines. If it is proven to be wrong, the function can be dropped.
The first implementation made annotate share diff configuration entries. But it
looks like users will user -w/b for annotate but not for diff, on both the
command line and hgweb. Since the latter cannot use command line entries, we
introduce a new [annotate] section duplicating the diff whitespace options.
