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/mbedTLS.vcxproj b/visualc/VS2010/mbedTLS.vcxproj
index 85dc3d8..0d24644 100644
--- a/visualc/VS2010/mbedTLS.vcxproj
+++ b/visualc/VS2010/mbedTLS.vcxproj
@@ -65,15 +65,19 @@
   <PropertyGroup Label="UserMacros" />

   <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>