Changing description of data.c file.
Again modifying data.c description. This file should contain
code for the flow of data through the PRES layer.
Adding TRUE and FALSE #defines.
Stubbing out PRES.graph.exists (task: 22).
Stubbed out SESS.dispatch.start (task: 24).
21. Write PRES.data.request.

Also added some PRES errors in bge-map-error.h.
Update agile.txt.
Renaming bge-map-error => bge-map-status. More descriptive.
Update file description of bge-map-status.h.