Refs #493: Install script was including the non-existent bhsearch wiki pages. Some changes on the trunk had been merged which shouldn't have been included in 0.5.1. Updated the install doc to mention that the virtualenv needs to include system site packages.

git-svn-id: https://svn.apache.org/repos/asf/bloodhound/branches/0.5@1465568 13f79535-47bb-0310-9956-ffa450edef68