[Proj] [MS Windows] PVALUE causes problems with mingw64compilers

[Howard Butler]

> On May 21, 2015, at 5:04 AM, sisyphus1 at optusnet.com.au wrote:
> 
> 
> Is it worth going to the trouble of changing the PVALUE symbol to (say) 
> PROJVALUE for mingw compilers only - but letting the PVALUE symbol stand 
> with non-mingw compilers:

I don’t think so. I think it should just be changed. The folks using projects.h have known it was a bit sketchy to be using (we tried to take it away once already). The next windows person using proj.4 with an interesting include scenario will run into again if we monkey patch the mingw case only.

Let’s just rename it, unless someone has a strong objection.

Howard