[XVS 3.9.221] Opening the iOS Build properties changes MtouchDebug on unmodified template projects


The symptoms of this bug are similar to bug 24150, but this bug is about the `MtouchDebug` property.

Regression status: Regression between 3.8.150 and 3.9.221.



## Steps to reproduce

1. Create a new iOS project, for example a "Visual C# -> iOS -> Classic API -> iPhone -> Blank App".

2. Wait for the template to finish loading.

3. Right click the project name in the Solution Explorer and select "Properties".

4. Note that the "iOS Build -> Debugging Options -> Enable Debugging" checkbox is empty and the tab shows an asterisk indicating something has changed.

5. Close the Properties pane.

6. Click the start debugging button to attempt to build and debug the app on device.



## Results

XamarinVS removes the "Enable Debugging" setting every time it opens the iOS project properties.


I suspect this corresponds to the `MtouchDebug` property in the `.csproj` file:
> <MtouchDebug>False</MtouchDebug>


This causes VS to display the following error message in an alert dialog after step 6:

> Microsoft Visual Studio
>
> Debug is not enabled in the current configuration. Please Start Without
> Debugging or change it in Properties -> iOS Build.



## Expected Results

Opening the project properties should not change the "Enable Debugging" setting.



## Version information

Microsoft Visual Studio Professional 2013
Version 12.0.30723.00 Update 3
Microsoft .NET Framework
Version 4.5.51641

### Bad
Xamarin   3.9.221.0 (a6d269d)
Xamarin.Android   4.20.0.34 (49a04b966feb40dfdba49d57ba16249b66d606a6)
Xamarin.iOS   8.6.0.0 (43e3b715220b50914b45bec675e19008ff50682a)

### Bad
Xamarin   3.9.228.0 (5f8a37f)
Xamarin.Android   4.20.0.34 (49a04b966feb40dfdba49d57ba16249b66d606a6)
Xamarin.iOS   8.6.0.0 (5d3de42232dc41c92a736286e33d9b3900a50dd7)

### Good
Xamarin   3.8.150.0 (10cfd178d55287f09c85f5a1e604dfe20889a40f)
Xamarin.Android   4.20.0.28 (ba9bbbdd44cfdc4bf485e8885bd2ad24fba525f7)
Xamarin.iOS   8.4.0.0 (840a925103a0bf4a856507f13d5eaee3c1579c2f)



## Additional information

Here's the full PropertyGroup for the "Debug|iPhone" configuration before and after opening the Properties tab.

### Before
> <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|iPhone' ">
>   <DebugSymbols>true</DebugSymbols>
>   <DebugType>full</DebugType>
>   <Optimize>false</Optimize>
>   <OutputPath>bin\iPhone\Debug</OutputPath>
>   <DefineConstants>DEBUG</DefineConstants>
>   <ErrorReport>prompt</ErrorReport>
>   <WarningLevel>4</WarningLevel>
>   <ConsolePause>false</ConsolePause>
>   <MtouchDebug>true</MtouchDebug>
>   <CodesignKey>iPhone Developer</CodesignKey>
> </PropertyGroup>

### After
> <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|iPhone' ">
>   <DebugSymbols>true</DebugSymbols>
>   <DebugType>full</DebugType>
>   <Optimize>false</Optimize>
>   <OutputPath>bin\iPhone\Debug</OutputPath>
>   <DefineConstants>DEBUG</DefineConstants>
>   <ErrorReport>prompt</ErrorReport>
>   <WarningLevel>4</WarningLevel>
>   <ConsolePause>false</ConsolePause>
>   <MtouchDebug>False</MtouchDebug>
>   <CodesignKey>iPhone Developer</CodesignKey>
>   <MtouchSdkVersion>8.1</MtouchSdkVersion>
>   <MtouchLink>SdkOnly</MtouchLink>
>   <MtouchProfiling>False</MtouchProfiling>
>   <MtouchExtraArgs />
>   <MtouchFastDev>False</MtouchFastDev>
>   <MtouchEnableGenericValueTypeSharing>True</MtouchEnableGenericValueTypeSharing>
>   <MtouchArch>Default, ARMv7</MtouchArch>
>   <MtouchUseLlvm>False</MtouchUseLlvm>
>   <MtouchUseThumb>False</MtouchUseThumb>
>   <MtouchUseSGen>False</MtouchUseSGen>
>   <MtouchUseRefCounting>False</MtouchUseRefCounting>
>   <MtouchOptimizePNGs>False</MtouchOptimizePNGs>
>   <MtouchI18n />
> </PropertyGroup>