CRM-13598 d6 - use  drupal mechanism to identify table prefixing

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* CRM-13598: User drupal {users} rather than storing name of drupal user table
  http://issues.civicrm.org/jira/browse/CRM-13598
CRM-13598 d6 user validation, This commit leaves the PEAR method on authenticate 'untouched' as there 'may' be cases where the bootstrapping is not taking place - although I am not convinced any remain, this remains a gotcha for people with prefixed tables in d6 & d7

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* CRM-13598: User drupal {users} rather than storing name of drupal user table
  http://issues.civicrm.org/jira/browse/CRM-13598
CRM-13598 d6 user vaauthentication - add comments

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* CRM-13598: User drupal {users} rather than storing name of drupal user table
  http://issues.civicrm.org/jira/browse/CRM-13598
Drupal user fns - copy Coleman's code in

https://github.com/civicrm/civicrm-core/pull/1798/files#r7022773
Drupal user fns - colemans' code
Merge pull request #1798 from eileenmcnaughton/4.4

CRM-13598 d6 - use  drupal mechanism to identify table prefixing