+ ~sync_nodes parameter: sync *only* these nodes from remotes (whitelist...

Hi,

I added an additional ~sync_nodes parameter that takes a list of node-names, similar to ~ignore_nodes. In case this list is non-empty, *only* nodes whose names start with any of these strings are synchronized, the value ~ignore_nodes is then ignored.

This optionally allows to only synchronize a limited predefined set of nodes, i.e. it kind of inverts the default case of synchronizing everything and excluding some.

Cheers, M.