edits to spec-uslab-introduction.xml

git-svn-id: http://gforge.hl7.org/svn/fhir/trunk/build@3663 2f0db536-2c49-4257-a3fa-e771ed206c19
edits to pract-uslab-introduction.xml

git-svn-id: http://gforge.hl7.org/svn/fhir/trunk/build@3664 2f0db536-2c49-4257-a3fa-e771ed206c19