Okay, detiails tonight as far as what ant tasks details to use. But here are the steps:
1. use xpath to read in Andorid.manifest vaules
2 Use propertyfile task to set new build number in a property file
3 read that value and use ReplaceRegEx to change it in the andorid.manifest.
If you want you can eliminate step 2 as you would still be using the xpath values to update your api doc to app version etc.