refactor Lexicon to reduce the redundant regular expression definition
Also add tight constraint for user data

Squashed commit of the following:

commit c77b5b37ee1db69e157bd20b2045fd1d8ecba2a0
Merge: 56077c0 622eb8b
Author: Seangchan Ryu <sryu@fnal.gov>
Date:   Mon Feb 3 15:42:54 2014 -0600

    Merge branch 'master' of https://github.com/dmwm/WMCore into lexicon_refactor

    Conflicts:
    	src/python/WMCore/Lexicon.py

commit 56077c0d2fe191a0b5a7de4b561681a861f17205
Author: Seangchan Ryu <sryu@fnal.gov>
Date:   Mon Feb 3 12:01:37 2014 -0600

    fix lexicon for dbs3