Look for curl and icu first in , if it's specified, before looking in...

Look for curl and icu first in , if it's specified, before looking in /usr/local and /usr, and after looking in the location specified in the --with-curl argument. Partial fix to #XERCESC-1892

git-svn-id: https://svn.apache.org/repos/asf/xerces/c/trunk@826941 13f79535-47bb-0310-9956-ffa450edef68