Add domain-based rate limiting to the HTTP checker module. The limit is currently set to 5 seconds between requests to the same domain on average, 2 seconds minimum.
 
 There is no UI for changing the rate limiting settings, but one could be added in a future version.

git-svn-id: https://plugins.svn.wordpress.org/broken-link-checker/trunk@880808 b8457f37-d9ea-0310-8a92-e5e31aec5664
Randomize the list of links that need to be checked to reduce the probability that it will contain multiple sequential links to the same domain. This helps avoid unnecessary request throttling.

git-svn-id: https://plugins.svn.wordpress.org/broken-link-checker/trunk@880811 b8457f37-d9ea-0310-8a92-e5e31aec5664