[po] Fix bad tag casing in nl.po

BXC6676 - HTML characters visible with Dutch language
[T4] Added nuspec
[NuGet] Fixed Bug 18951 - Incorrect path separator used for Import.

https://bugzilla.xamarin.com/show_bug.cgi?id=18951

Incorrect path separator used when adding MSBuild .targets/.props
file to a project when installing a NuGet package. On the Mac the
forward slash character was being used for the path to the .targets
file. All paths in MSBuild project files should use backslash on
all platforms. If forward clashes are used then updating a NuGet
package on Windows will fail to remove the old import from the
project. It will also cause the build to fail since the path is
resolved to a directory inside Program Files.
[NuGet] Remove forward slash imports when updating a package.

Fixes Bug 20610 - Xamarin Forms samples will not build on Windows
even after package update.
https://bugzilla.xamarin.com/show_bug.cgi?id=20610

On uninstalling or updating a NuGet package, .targets file imports
are removed from the project if they contain forward slashes and if
they contain backslashes. This allows the project to fix itself
without requiring manual editing of the MSBuild project file.
Fix  20533 - Project Reference 'properties' is showing disabled
[MSBuild] Add extension point for global properties

Also unifies setting core global properties.
[MSBuild] Remote builder support for arbitrary target/item evaluation

Not exposed yet, but used for reference evaluation.
[Core] Fix recursive includes for custom MSBuild frameworks
[Core] Filter overridden assemblies from chains of framework includes

And fix up refreshing/reloading stuff as appropriate.
[Ide] Fix crash when loading pads

When registering a new pad as a result of the installation of a new add-in
the corresponding DockItem was not created. This is now done.

Fixes bug 20600 - Installing an addin that creates a new pad throws a null
reference exception and crashes Xamarin Studio.
[Core] Properly load projects with ids without curly braces

Fixes bug 20618 - Adding F# project fails to put project identifier in curly
braces in solution file.
[Core] Allow a Condition to be set for an MSBuild Import.

A condition specified in the call DotNetProject.AddImportIfMissing(..)
will now be saved in the MSBuild project file. This allows imports to
be conditional.

One use is for NuGet packages that define a custom MSBuild targets
file and allows the targets file to be conditionally imported if the
file exists.

<Import
  Project="packages\Xamarin.Forms\Xamarin.Forms.targets"
  Condition="Exists('packages\Xamarin.Forms\Xamarin.Forms.targets')"/>

Using the Exists check allows Visual Studio to open the project when
the package is missing and has not yet been restored.
[NuGet] Add Condition to an Import added by a NuGet package.

If a NuGet package adds an import for a custom MSBuild .targets or
.props file then these are added to the project file with a Condition
attribute that checks that the file exists.

<Import
 Project="packages\Xamarin.Forms.1.1.0\build\net45\Xamarin.Forms.targets"
 Condition="Exists('packages\Xamarin.Forms.1.1.0\build\net45\Xamarin.Forms.targets')" />

If this check is not added then Visual Studio will not be able to load
the project if the NuGet packages are not restored.
[NuGet] Fix repositories.config file not being restored.

Force the creation of the repositories.config file after the packages
have been restored by creating NuGet Package Managers for each
project.

The repositories.config file is used by NuGet to determine which
projects share the packages directory. All projects, in a solution,
that have NuGet packages should have an entry in the
repositories.config file. If the repositories.config file is missing,
or a project does not have an entry in the file, then NuGet may remove
a NuGet package from the packages directory after uninstalling it from
one project since it believes no other projects in the solution are
using that NuGet package and it can safely be removed completely.
Fixed 'Bug 19837 - Blank Editor tabs - File name not always
displayed'.
This is not really a fix - it's just a work around.
[tests] Write out xml results files for every test fixture

They are in the format TestResults_ASSEMBLYNAME.log
Use the .xml extension

Note: These files will be written to main/tests/*
Ignore main/tests/TestResult*.xml files.
Run all test fixtures instead of exiting eagerly.
TestResults_*.xml -> TestResult_*.xml for consistency with e.g. Mono's test suite.