This module contains functions governing the assignment of version numbers, patterned after Ubuntu version number policy:

1. To distinguish packages which have been pulled out of one vendor's repository to build for another, we add a vendor name and a build number, so version 1.2-3 becomes 1.2-3vendorname1. Subsequent builds (perhaps due to changes in build dependencies) would be numbered 1.2-3vendorname2 and so on.
2. In addition, packages which are backported, (i.e. built for a non-development release such as Debian etch or Ubuntu feisty) need another tag to distinguish them from the version that would go into the development release (sid or, as of this writing, heron.) So if we pulled the source for version 1.2-3vendorname4 out of our pool to build for feisty, it would become 1.2-3vendorname4~feisty1.
3. The first two policies combine if we are building a package pulled directly from the other vendor into our feisty pool, then 1.2-3 would become 1.2-3vendorname0~feisty1. Subsequent builds of 1.2-3 (perhaps due to changes in build dependencies) would get increasing build numbers, 1.2-3vendorname0~feisty2 etc.
4. If the original version number does not end with a digit, a 0 is inserted before the vendor name to facilitate parsing of these tags.
5. Finally, an additional tag format is supported for the benefit of one autobuilder client, where before the vendor name an r and an integer are inserted.