Also update BUILD.txt

Move the upgrade function first and check explicitly for the old ldb name.
Perform upgrades up to v02 first if necessary.
Then proceed as normal letting the normal init functions perform further
upgrades if necessary.
This now works also if there is no "local" provider in the current
configuration.

We were never filling the group attrs because of an inverse return check.
Plus fix a crash bug for using a pointer that is not a memory context.

This task allows us to rebuild memberuid and memberof attributes throughout the
database. This way we can upgrade from version 0.4 databases that didn't
generate and store memberuid.
The task can be invoked by adding a speaicl named entry to the ldb file.
The entry dn to use is: @MEMBEROF-REBUILD, the entry has no attributes and any
attribute is ignored at present.
The entry will not be stored in the database but will just trigger the task to
execute a rebuild of the memberof and memberuid attributes

Search the local db to find the local DN using the original DN as search key.
This way we do not have to rely on weak and faulty heuristicts based on DN
names.
Add a few helper functions in the process and change the way we pass members to
sysdb_store_group_send(), instead of passing users and groups list, just add
member DNs to the other sysdb attrs.