NuGet allows a solution to override the standard packages directory
with a repositoryPath setting in the NuGet.config file at the solution
level in the .nuget directory.
<configuration>
<config>
<add key="repositoryPath"
value="../../MyPackages" />
</config>
</configuration>
This is now supported by SharpDevelop.
If a solution has its own NuGet.Config file this will be read and
any package sources defined in this file will be available in the
list of package sources in the Manage Packages dialog.