[MERGE] Fix reconfiguring standalone tree to lightweight checkout

[Ian Clatworthy]

Ian Clatworthy has voted tweak.
Status is now: Conditionally approved
Comment:
The help for reconfigure needs to be expanded to explain when this 
particular transformation will work and when it won't. Also add a NEWS 
entry please.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C4761616C.5010204%40utoronto.ca%3E