* added missing return statements
* only spend up to 10 seconds for initially fetching the list of collections in arangosh
fetching the list of collections is a blocking operation, and the default timeout for this is very high.
If the server is blocked by whatever reason, then the shell is unusable until the collections list request returns.
To avoid this, the initial request is limited to 10 seconds, so the shell can be used afterwards.
* if an index cannot be used for sorting, its sort
cost was previously returned as 0. this will in fact favor
indexes that can be used for filtering but not for sorting
over indexes that can be used for both.
this change is to report the sort cost for indexes that
cannot be used for sorting to n * log(n), where n is the
number of documents that optimizer expects to come out of the
index after filtering