Make Jeremy Siek the maintainer of the concepts lib

[SVN r30958]

libs/maintainers.txt

@@ -4,7 +4,7 @@ any
 array
 assign                Thorsten Ottosen <nesotto -at- cs.auc.dk>
 bind                  Peter Dimov <pdimov -at- mmltd.net>
-concept_check
+concept_check         Jeremy Siek <jgs3847 -at- cs.rice.edu>
 config                John Maddock <john -at- johnmaddock.co.uk>
 conversion
 crc