Allow passing of context data to async dbus method call reply handlers

Add new function dbus_send_ex() that is similar to already existing
dbus_send() function, except it takes extra user_data and user_free
parameters.
Cache dbus name owner identification data for debugging purposes

Textual identification of dbus name owner can be requested via
two new functions: mce_dbus_get_name_owner_ident() and
mce_dbus_get_message_sender_ident().

If requested name is not already known, the functions will - after
initiating asynchronous pid query - return only the dbus name for
use at the call site.

Once the async pid query finishes, the command name is resolved
from /proc file system and full information is logged so that
previously written log entries can be associated with a command.

Subsequent calls will immediately provide full information for use
at the call site.

If the identified name drops from system bus, the cached entry is
released.
Fix removing of dbus handlers while iterating over handler list

Upon receiving a dbus message, the list of dbus handlers is iterated
and callback functions of matching handlers get called. If the handler
callback does a self remove, the iterated list is modified at the
iteration point.

There was a workaround for this in place, but it did not work properly
and made the iterator skip the entry after the removed one - which could
cause subtle errors.

To fix this mce_dbus_handler_remove() still removes the handler object,
but leaves the now dataless link object in place. The stale link objects
are then cleaned up after finishing the list iteration.
Identify processes that do dbus ipc with mce

This happens by default on mce devel builds, otherwise mce must be
executed in verbose mode.

[mce] Identify processes that do dbus ipc with mce
Demote/remove development time logging
Do not use quote chars in dbus owner identification string

Makes it a tiny bit more compact. And since the string length is limited,
we might end up cutting of the final quote char anyway.
Fix memory leak in mce_dbus_ident_delete()
Remove name owner information before cleaning up dbus connection

The name owner tracking uses dbus handlers, and those must be removed
before generic handler cleanup or connection closing.
Fix memory leak in gconf_value_set_from_string()
Add atexit handler for builtin-gconf module

Releasing the default_client data makes it easier to detect possible
memory leaks.
Merge pull request #130 from spiiroin/dbus_sender_info

Identify processes that do dbus ipc with mce