drsyms windows symbol store support

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on May 06, 2011 13:13:59_

looks like SymInitialize can take an explicit path, or it will use the
_NT_SYMBOL_PATH env var. but, looks like will ignore src\* paths: need to
use symsrv.dll for those to work.
symsrv.dll is NOT in the DDK.
symsrv.dll is listed in redist.txt just like dbghelp.dll.

to get dbghelp.dll symbol store support working in-process with the private
loader, need to hook priv kernel32's GetModuleFileName. note that the
symsrv dll goes and loads over 45 libraries so maybe we don't really want
it in-process for most clients: xref sideline options ( issue #446 ).

drsyms today supports _NT_SYMBOL_PATH pointing at a local directory of
cached files retrieved earlier (via windbg, e.g.)

there are also some issues with a license agreement when connecting to
Microsoft's symbol server: symsrv pops up a dialog box and then stores a
symserv.yes file to avoid it in the future.

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=450_