Document the length restrictions on the username and password for
	src/support/htpasswd.  Also gritch about illegal characters in
	the username (':' is the field separator).


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@83275 13f79535-47bb-0310-9956-ffa450edef68