Update configuration to local/user level if original entry is from local too

[kzu]

Given:

• When using Configuration extensions
• Hierarchical config files
• A local value from a .netconfig.user

When:

• Configuration value is updated

Then:

• Value should be updated on the .user file where the original value was read from

Motivation:

• If the value was stored to the default location (the .netconfig file by default), a subsequent read would result in the unintuitive situation that the "old" local value would still be there, taking precedence over the just updated value, because it was saved to a lower-precedence files.