fixing exiv2.vsprops to work on Visual Studio 2010

git-svn-id: svn://dev.exiv2.org/svn@3133 b7c8b350-86e7-0310-a4b4-de8f6a8f16a3
Refactor EXIV2_HTTP_POST, it's more flexible and it is required for http/https write access.

git-svn-id: svn://dev.exiv2.org/svn@3134 b7c8b350-86e7-0310-a4b4-de8f6a8f16a3