Main/HostDnsService: fix fallout from previous (r99529).

Main/HostDnsService: use <iprt/cpp/lock.h> instead of a roll-your-own version.

Main/HostDnsService: instead of keeping fragile state g/c notifyAll() and just notify proxy directly from setInfo() when info changed.

Main/HostDnsService: revert r96327 and follow-up r96329 and r96331 to revert conversion of HostDnsInformation to Unicode. HostDnsServiceWin.cpp behavioral changes will be redone as a separate commit against old definition of HostDnsInformation. Intervening SafeArray cleanup in r96372 is preserved, hopefully without errors. Please review.

Main: trailing spaces + warning

Main: DnsMonitorService: step on unicode rails: store network configuration in unicode-compatible containner (std::wstring) (preliminary tested on Linux, Mac and Windows); DnsMonitorService for Windows: reworked in order to subscribe to correct events and filter-out those ones we don't interested in. (Experimantal, needs more testing and review).

Main/HostDnsService: - Generic part could be used with threading on or off: OS which can monitor changes on DNS structures might need this (e.g. Windows, Darwin, Linux) - ResolvConf based (Linux, Solaris, FreeBSD ans Os/2) doesn't use scanf based resovl.conf parsing new Slirp's parser used instead. It's configured to provide strings instead of addresses. (to resolve xtracker/7034c2) - Darwin monitoring code has been refactored. - linux changed to handle cases described in xtracker/7034c3 - Windows monitors changes on register changes.

spaces

Main/HostDnsServiceDarwin: parent has been changed HostDnsService -> HostDnsMonitor::init();

Main/HostDnsServiceDarwin.cpp: no this in static method.

Main/HostDnsServiceDarwin: build fix.

Main/HostDnsService: splits HostDnsService on "singleton" HostDnsMonitor which monitors host changes and share DnsInformation to per HostImpl/VirtualBoxImpl objects HostDnsMonitorProxy. TODO: Win/Darwin parts might burn (not tested) TODO: find good place to call HostDnsMonitor::shutdown() to stop monitoring thread. (ref counting could be used on HostDnsMonitor::addMonitorProxy and HostDnsMonitor::releaseMonitorProxy, but it better to pausing monitoring on no --auto-shutdown launches of VBoxSVC).

Main: Whitespace (including tabs!) and svn:keywords cleanups by scm.

Main: HostDnsServiceWin::init(void) -> HostDnsServiceWin::init(const VirtualBox *aParent) and firing event on update.

HostDnsServiceDarwin::update() don't panic if host hasn't got networking.

hostMonitoringRoutine: warnings.

hostMonitoringRoutine: warnings [-Wunused-parameter]

HostDnsServiceDarwin: listener for host's DNS configuration update.

header fixes

Main/DNS: general host specific DNS and Co handling added. Darwin implementation has self-update mechanism, for other hosts it's in todo list.