Now, the daemon will check that a base directory is NOT reached via

Now, the daemon will check that a base directory is NOT reached via
symbolic link.  Documentation added to illustrate the restriction.

This allows several simplifying (and performance-enhancing) assumptions to
be made elsewhere in the code:

 * it ensures that paths resolved in the client via realpath() will match
   our data structure keys

 * it's possible to generate the correct absolute path when given a
   relative path by simply prepending the base directory

 * it's not necessary to resolve paths that begin with '/'
 -- kevin

git-svn-id: svn://svn.oetiker.ch/rrdtool/trunk@1603 a5681a0c-68f1-0310-ab6d-d61299d08faa