CTR: docs
Merged revision 1061503 from tomcat/trunk:
Clarify when docBase can be set
It fixes https://issues.apache.org/bugzilla/show_bug.cgi?id=50441


git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc6.0.x/trunk@1457374 13f79535-47bb-0310-9956-ffa450edef68