Add ability to place named variables in language strings [J2.5]

http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=31587

This is the Joomla 2.5 PR of #880 & #1597
 # [#31681] Module manager allows positions with trailing spaces. Thanks
Richard McDaniel
(Fix #1582)
 #$ [#31631] Small typo fix in Plugin. Thanks Gunjan Patel and Tobias
Zulauf
(Fix #1646)
 # [#27824] Offline image overflow. Thanks Angelika Reisiger
(Fix #1169)
 $ [#30664] User Categories helps screen strings missing. Thanks George
Wilson
(Fix #1702)
sql error
Merge remote-tracking branch 'remotes/upstream/2.5.x' into patch-3
Merge pull request #1599 from nonumber/patch-3

Add ability to place named variables in language strings [J2.5]
Check for the onUserAuthenticate function before calling it.