there's a single GUI_HTTP object,
and it works only if used sequentially,
i.e. an op is started only after the previous one ends.
This breaks if a GUI RPC triggerse and op while
a project-list fetch (initiated by the client itself) is in progress.
Or if two managers are connected at the same time,
and both do HTTP ops.
The solution: have a separate GUI_HTTP object for each GUI_RPC_CONN,
and an additional one for use by the client itself.
svn path=/trunk/boinc/; revision=13692