Modify NuPack.Tools to not build vsix if VSSDK not installed but still allows project to be loaded.
Modify NuPack.Tools to not build vsix if VSSDK not installed but still allows project to be loaded.

jholovacs/NuGet,alluran/node.net,atheken/nuget,mrward/NuGet.V2,kumavis/NuGet,xoofx/NuGet,alluran/node.net,antiufo/NuGet2,GearedToWar/NuGet2,anurse/NuGet,antiufo/NuGet2,dolkensp/node.net,indsoft/NuGet2,indsoft/NuGet2,GearedToWar/NuGet2,oliver-feng/nuget,atheken/nuget,OneGet/nuget,indsoft/NuGet2,indsoft/NuGet2,ctaggart/nuget,xoofx/NuGet,rikoe/nuget,indsoft/NuGet2,mono/nuget,ctaggart/nuget,RichiCoder1/nuget-chocolatey,GearedToWar/NuGet2,themotleyfool/NuGet,jmezach/NuGet2,GearedToWar/NuGet2,oliver-feng/nuget,antiufo/NuGet2,alluran/node.net,xero-github/Nuget,dolkensp/node.net,anurse/NuGet,mrward/nuget,mrward/NuGet.V2,alluran/node.net,GearedToWar/NuGet2,chocolatey/nuget-chocolatey,mrward/nuget,pratikkagda/nuget,antiufo/NuGet2,RichiCoder1/nuget-chocolatey,chester89/nugetApi,mrward/NuGet.V2,mono/nuget,jmezach/NuGet2,themotleyfool/NuGet,pratikkagda/nuget,GearedToWar/NuGet2,indsoft/NuGet2,OneGet/nuget,oliver-feng/nuget,mrward/NuGet.V2,jmezach/NuGet2,akrisiun/NuGet,oliver-feng/nuget,chocolatey/nuget-chocolatey,jmezach/NuGet2,mrward/nuget,xoofx/NuGet,antiufo/NuGet2,mrward/NuGet.V2,mrward/nuget,OneGet/nuget,RichiCoder1/nuget-chocolatey,xoofx/NuGet,oliver-feng/nuget,chocolatey/nuget-chocolatey,mrward/nuget,rikoe/nuget,jmezach/NuGet2,xoofx/NuGet,mono/nuget,chocolatey/nuget-chocolatey,pratikkagda/nuget,pratikkagda/nuget,mrward/nuget,antiufo/NuGet2,zskullz/nuget,zskullz/nuget,kumavis/NuGet,zskullz/nuget,chocolatey/nuget-chocolatey,mono/nuget,mrward/NuGet.V2,dolkensp/node.net,chester89/nugetApi,OneGet/nuget,pratikkagda/nuget,ctaggart/nuget,RichiCoder1/nuget-chocolatey,jmezach/NuGet2,dolkensp/node.net,jholovacs/NuGet,ctaggart/nuget,RichiCoder1/nuget-chocolatey,chocolatey/nuget-chocolatey,rikoe/nuget,pratikkagda/nuget,xoofx/NuGet,themotleyfool/NuGet,RichiCoder1/nuget-chocolatey,jholovacs/NuGet,oliver-feng/nuget,zskullz/nuget,jholovacs/NuGet,jholovacs/NuGet,rikoe/nuget,jholovacs/NuGet,akrisiun/NuGet