Update of the Visual Studio files

Contains additional project file, ecdh_curve25519.vcxproj, as well as fix
for intermediate files causing the warning MSB8028 with Visual Studio 2015.
diff --git a/visualc/VS2010/rsa_decrypt.vcxproj b/visualc/VS2010/rsa_decrypt.vcxproj
index 67404ef..fb3f444 100644
--- a/visualc/VS2010/rsa_decrypt.vcxproj
+++ b/visualc/VS2010/rsa_decrypt.vcxproj
@@ -71,18 +71,22 @@
     <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />

   </ImportGroup>

   <PropertyGroup Label="UserMacros" />

-  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">

-    <LinkIncremental>true</LinkIncremental>

-  </PropertyGroup>

-  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">

-    <LinkIncremental>true</LinkIncremental>

-  </PropertyGroup>

-  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">

-    <LinkIncremental>false</LinkIncremental>

-  </PropertyGroup>

-  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'">

-    <LinkIncremental>false</LinkIncremental>

-  </PropertyGroup>

+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
+    <LinkIncremental>true</LinkIncremental>
+    <IntDir>$(Configuration)\$(TargetName)\</IntDir>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
+    <LinkIncremental>true</LinkIncremental>
+    <IntDir>$(Configuration)\$(TargetName)\</IntDir>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
+    <LinkIncremental>false</LinkIncremental>
+    <IntDir>$(Configuration)\$(TargetName)\</IntDir>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'">
+    <LinkIncremental>false</LinkIncremental>
+    <IntDir>$(Configuration)\$(TargetName)\</IntDir>
+  </PropertyGroup>
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">

     <ClCompile>

       <PrecompiledHeader>