Updated SymEngine.cpp (see extended desc)

1. Added support for following Windows versions:

+ Windows XP Professional x64 Edition
+ Windows 7
+ Windows 8
+ Windows 8.1
+ Windows Home Server
+ Windows Server 2003 R2
+ Windows Server 2008
+ Windows Server 2008 R2
+ Windows Server 2012
+ Windows Server 2012 R2

For details see
http://msdn.microsoft.com/en-us/library/windows/desktop/ms724833(v=vs.85).aspx

2. GlobalMemoryStatus call in CSymEngine::GetMemInfo replaced to
GlobalMemoryStatusEx in order to detect correct memory info on computers
with more than 4 GB of memory.