followup for HER-1688 remember external job directories

* Engine.java
    suppress WARNING for common case of harmless failure during rescans: job already exists
* EngineResource.java
    suppress rescan on each reload (ODD: steve had already committed this change -- I got the commit email -- but now the repo version is missing it. Sourceforge problems?)

engine/src/main/java/org/archive/crawler/framework/Engine.java

@@ -97,6 +97,9 @@ public class Engine {
                 // convert .jobpaths to the referenced external directory
                 jobFile = getJobDirectoryFrom(candidateFile);
             }
+            if (jobConfigs.containsKey(jobFile.getName())) {
+                continue;
+            }
             if(!addJobDirectory(jobFile)) {
                 LOGGER.log(Level.WARNING,"invalid job directory: " + jobFile 
                         + " where job expected from: " + candidateFile);

engine/src/main/java/org/archive/crawler/restlet/EngineResource.java

@@ -232,8 +232,6 @@ public class EngineResource extends BaseResource {
         
         ArrayList<CrawlJob> jobs = new ArrayList<CrawlJob>();
         
-        // re-scan job configs on each page load
-        engine.findJobConfigs();
         jobs.addAll(engine.getJobConfigs().values());
          
         pw.println("<form method=\'POST\'><h2>Job Directories ("+jobs.size()+")");