- Add 'simple' implementation of MmDbgCopyMemory to read/write virtual memory in...

- Add 'simple' implementation of MmDbgCopyMemory to read/write virtual memory in a somewhat safe way (still no support for physical memory). Properly implement KdpCopyMemoryChunks as a wrapper around MmDbgCopyMemory and make most of the remaining unsafe copies use it instead of RtlCopyMemory. This fixes most of the remaining crashes during KD debugging as WinDbg/KD relies on the kernel support to handle bad addresses.
- Stub out the remaining missing global variables for the debugger data block -- fixes some cases of WinDbg failures and gives it a chance to handle errors instead of failing on a NULL read. Several of these variables are for functionality we don't yet implement, so I tried to put them where they are "least wrong". Everything besides the MmLoadedUserImageList variable is left unitialized -- KD should mostly be able to handle this properly.
- Define correctly sized KDDEBUGGER_DATA64 for our kernel (needs to be done in a better way).

svn path=/trunk/; revision=43863