[Libguestfs] [PATCH nbdkit v2] common: Move shared bitmap code to a common library.

[Richard W.M. Jones]

This is exactly the same as v1:

https://www.redhat.com/archives/libguestfs/2018-December/msg00004.html

except that it now frees the bitmap on unload (which the old code did
not - there was always a memory leak).

Rich.