3.3.9 build error in SquidString.h

[Amos Jeffries]

As some of you know I have been working with a sponsor to get Windows 
builds going again this year.

Visual Studio is giving me a strange error though in our SquidString.h code:
   error C2057: expected constant expression
this is occuring on the code line:
   statis const size_type npos = std::string::npos;

any ideas about how to solve this one properly? for now we are having to 
just define it as -1 by looking up the VC header files definitions of 
std::string::npos manually.

Amos