Restore correct public interface of getUserData() for authldap
plugin

The outer/public getUserData() implemented as a wrapper for the
previous fn which is now protected.
Allow user info to be retrieved without groups

Some parts of dokuwiki (e.g. recent changes, old revisions) can
requests lots of user info (to provide editor names) without
requiring any group information.

This change also implements caching of user info by authmysql &
authpgsql plugins to avoid repeated querying of the DB to retrieve
the same user information.
code styling - add missing braces
fix comment errors, sp. & grammar
use $requireGroups constants in auth classes; comments; code improvements
KISS - remove class constants for REQUIRE_GROUPS & IGNORE_GROUPS and replace with boolean values
Merge remote-tracking branch 'origin/auth_getUserData_improvements'

* origin/auth_getUserData_improvements:
  KISS - remove class constants for REQUIRE_GROUPS & IGNORE_GROUPS and replace with boolean values
  use $requireGroups constants in auth classes; comments; code improvements
  fix comment errors, sp. & grammar
  code styling - add missing braces
  Allow user info to be retrieved without groups
  Restore correct public interface of getUserData() for authldap plugin

Conflicts:
	inc/common.php