close ldap connections when pool it is stopped
add stop function to some core modules
allow to register/unregister virtualhosts
add reload function to gen_mod
reload config command
add stop function to auth modules
fix config change function
* get config filename from commandline parameters
* improve error reporting
* backup old config files
* ignore some changes, which don't require restart like acl
delete only local processes while stoping eldap pool
allow to stop db backend without checking local options
fix override config strategies and restarting rdbms and auth systems
don't replace node_start entry
check config version on running node, fix listeners restart
fix local_config grouping
restart only listeners that have changed
Remove sending conf file while reloading cluster; add local only reload

The commands that are now available in the mongooseimctl are:
* reload_local
* reload_cluster.
The commit also removes making backups of existing config files
introduces some refactorings.
Close client connections to domain to be removed; verify the config file

Now all the client connections associated with a domain to be removed
are closed. Additionally, a config file on each node is compared to the
one on the initiating node.

The whole cluster reload mechanism works as follows:
1. Parse the configuration file on the initiating node.
2. Compute a diff between current configuration and the one read from
   the provided file
3. Compute a hash of the current node's configuration (config version)
4. Compute a hash of the new configuration read from file (file version)
5. Apply new configuration on the current node
6. Send configuration diff computed on the initiating node to other nodes
   along with the config version, file version and the file path
7. Compute config version and file version (after parsing it) on the
   other nodes and verify that they match their counterparts from
   the initiating node; if any doesn't match cancel the operation
8. Apply the configuration diff on the other nodes
Fix computing file and config versions that are compared between nodes
Export config checksumming functions for testing

(cherry picked from commit 985b1f271cd7210955b7cee02311bf0b499048ba)
Delimit functions in a sane way

(cherry picked from commit 4a4f583abafd8e9d72eb65c1220a51a9d7b0dd29)
Extract loops over options to standalone functions

(cherry picked from commit e604ff204b41d0b36d3e6a8a375b5c0d67b7c290)
(cherry picked from commit bc8b07b6f78ea54e78f04f432da2b74c439dfe11)