Fix data handling
The length should be exactly the same as the data, for example if the
data is "hello" only 5 characters should be written on the stream. Thus
it should always be `len(data)`, not `len(data)+1` as it currently is in
some places.
Since the first commit of hg2git.py there was a wtf comment, presumably
Rocco was confused about this common discrepancy.
We can shuffle the logic around by adding '\n' to the data, and removing
+1 to the length.
Also, the data should be written without a newline (wr_no_nl).
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>