Nuget binary packages do not respect conditional rules from paket.dependencies file

Description

Nuget binaries do not respect conditional rules from the paket.dependencies file, in at least one scenario. This prevents us from using the Vsxmd package with Paket, which allows a windows dev machine to generate markdown from xml comments automatically on build. Our Linux build machine cannot run exe files, and because the conditional rules do not work, we cannot disable this in release mode, and therefore this package cannot be used with Paket.

See https://github.com/fsprojects/Paket/issues/197 and https://github.com/fsprojects/Paket/issues/1026 for related features.

Repro steps

In a new project, edit paket.dependencies, and include the following:
nuget Vsxmd condition:DEBUG

In paket.references, include: Vsxmd

Expected behavior

foo.fsproj file should contain:
<Import Project="..\..\packages\scripting\Vsxmd\build\Vsxmd.targets" Condition="'$(DEBUG)' == 'True' And Exists('..\..\packages\scripting\Vsxmd\build\Vsxmd.targets')" Label="Paket" />

Actual behavior

foo.fsproj file contains:
<Import Project="..\..\packages\scripting\Vsxmd\build\Vsxmd.targets" Condition="Exists('..\..\packages\scripting\Vsxmd\build\Vsxmd.targets')" Label="Paket" />

Known workarounds

None

Run the repro using paket.dependencies with nuget Vsxmd condition:DEBUG and the Vsxmd entry in paket.references, then inspect how Paket generates the foo.fsproj import. Compare the actual import condition with the expected DEBUG and Exists conditions; done means the generated project preserves the conditional rule for NuGet binary packages.