This patch fixes some minor issues with the Windows config.h and TargetVersion.h files.
_WIN32_WINNT (and thus WINVER) was being forced to 0x0601, overriding project-specific settings. The generally accepted approach is to let the project set this and only define it if it's not already present.
struct pollfd must be defined for a true XP compatible build (WINVER 0x501). This could not happen before when WINVER was being forced to 0x0601, causing the struct definition to be pulled in from a Vista+ header.
Some other tweaks resolve compiler warnings.
I've tested this by building the Thrift C++ libraries with VS2010, as well as our Windows projects that use Thrift. Please provide feedback if this causes any issues.