print the FB JSON error message

If the HTTP GET to https://graph.facebook.com/oauth/access_token fails,
the plugin will print the error message...

SpringSecurityFacebookGrailsPlugin.groovy

@@ -29,7 +29,7 @@ import com.the6hours.grails.springsecurity.facebook.FacebookAuthRedirectFilter
 
 class SpringSecurityFacebookGrailsPlugin {
 
-    String version = '0.14.5pg2'
+    String version = '0.14.5pg4'
 
     String grailsVersion = '2.0.0 > *'
     Map dependsOn = ['springSecurityCore': '1.2.7.2 > *']

plugin.xml

@@ -1,4 +1,4 @@
-<plugin name='spring-security-facebook' version='0.14.5pg2' grailsVersion='2.0.0 &gt; *'>
+<plugin name='spring-security-facebook' version='0.14.5pg4' grailsVersion='2.0.0 &gt; *'>
   <author>Igor Artamonov</author>
   <authorEmail>igor@artamonov.ru</authorEmail>
   <title>Facebook Authentication for Spring Security</title>

src/groovy/com/the6hours/grails/springsecurity/facebook/FacebookAuthUtils.groovy

@@ -133,9 +133,21 @@ class FacebookAuthUtils {
 
     FacebookAccessToken requestAccessToken(String authUrl) {
         try {
+			log.debug "Getting the access token for URL $authUrl"
             URL url = new URL(authUrl)
-            String response = url.readLines().first()
-            //println "AccessToken response: $response"
+			HttpURLConnection connection = (HttpURLConnection) url.openConnection()
+			String response 
+			if (connection.responseCode == HttpURLConnection.HTTP_OK){
+				response = connection.getInputStream().readLines().first()
+			}else{
+				String error = connection.getErrorStream().getText()
+				log.error "Failed to get the access token when requesting $authUrl. Error is $error"
+				return null
+			}
+
+
+            log.debug "AccessToken response: $response"
+
             Map data = [:]
             response.split('&').each {
                 String[] kv = it.split('=')