waf-abi: auto-generate per-symbol versions from ABI files

waf-abi: auto-generate per-symbol versions from ABI files

This changes our version-script generation to use the ABI files that
are saved in git with each version number change of our public
libraries.

We use these ABI files to generate a linker version script that gives
the exact version number that each symbol was introduced. This
provides us with automatic fine grained symbol versioning.

Pair-Programmed-With: Jelmer Vernooij <jelmer@samba.org>
Pair-Programmed-With: Andrew Bartlett <abartlet@samba.org>