keithbostic and michaelcahill please review this. This fixes the specific issue in WT-1439.

This cuts the time in my test from 84 seconds to about 4.5 seconds for 3000 tables. I created a new, slightly different version,{{ __wt_conn_btree_apply_uri}} that applies the function to any dhandle that matches the URI. This avoids walking the entire conn->dhandle list to then walk the session list to then call the function on all URIs and have it be a no-op since the URI does not match the one we're interested in.