This update is required by the ldb update which is required by the samba
update to 4.1.11.

- Require pkg-config from the devel packages.

- Update to 2.1.1.
+ documentation updates
+ a fix for pytalloc-util.pc
+ performance improvements here and there
+ fixed compiler warnings

- Remove dependency on doxygen. Doxygen is only used for generating
the html documentation, but the html documentation was not
actually packaged, so there is no point in running it.

- Remove dependency on gpg-offline to reduce rebuild times; signature checking
is implemented already in the source validator.

- Update to 2.1.0.
+ Add talloc_pooled_object and test it
+ Allow nested pools
+ Add a separate pool size
+ Put pool-specific data before the chunk
+ Introduce __talloc_with_prefix
+ Decouple the dual use of chunk->pool
+ Only provide the --enable-talloc-compat1 in standalone build
+ Simplify _talloc_free_poolmem a bit

- Verify source tar ball gpg signature.