[GRASS5] d.graph updates

[Hamish]

Hi,

I've done a little cleanup on the d.graph module.

No big enhancements like adding support for symbols, but it now has
better error handling, debug info and will survive d.redraw if input was
given from a file. Added an updated version of grass.logo.sh from the
GRASS 5 source into the module's source dir as an example. Also added a
command to set the text rotation.

I didn't bother to do the same updates to d.mapgraph as I plan on
merging it into the d.graph module as the "-m" flag. In regards to that
effort, if anyone wants to merge the malloc -> G_malloc changes, please do!


Hamish