4.4 bugs

[emgarten]

Triage and find high priority issues for 4.4

• Add different msbuild task UserAgent strings for netcore vs desktop #5709 Add different msbuild task UserAgent strings for netcore vs desktop
• Failed to restore packages after switch to the new project system #5630 Failed to restore packages after switch to the new project system
• Read PackageReferences from CollectPackageReferences #4967 Read PackageReferences from CollectPackageReferences
• Assets file should use relative paths to enable moving projects more easily #4582 NuGet should should burn in assets file relative to project to prevent broken projects when they are moved on disk
• Filename or extension is too long. #4931 Filename or extension is too long
• nuget.exe install TargetFramework support #5736 nuget.exe install TargetFramework support
• Nuspec files should be read once per restore #5735 Nuspec files should be read once per restore
• Nuget.exe (3.+) install package with Version number and ExcludeVersion flag doesn't update package to newer version #2405 Nuget.exe (3.+) install package with Version number and ExcludeVersion flag doesn't update package to newer version
• nuget.exe install incorrectly disables caching #5737 nuget.exe install incorrectly disables caching