Attached a patch for the rrd-tool LIBDBI integration with the following improvements:

a) correct error handling in case of libdbi being unable to load the driver
   was producing segmentation faults.

b) better parsing of datasources

   * until now timestamp fields had to be integer and had to contain a unix
     timestamp - now you can now also use DateTime fields (you still need to
     specify it, as the time-range needs to be defined correctly)

   * data fields are now no longer limited to (var)char or DOUBLE fields -
     FLOAT, INTEGER,... are now also supported.

c) there is a bug with at least LIBDBI 0.8.1 in conjunction with mysql that
   can result in segmentation faults when BINARY/BLOB fields are accessed -
   rrdtool will now tell you about this fact before dying ;)

d) also the value of rrdderivemaxstep only gets applied if derive has been
   selected correctly.

e) "GROUP BY timestamp" has been removed from SQL statement.

f) "ORDER BY timestamp" will be added only in the case of fetching "derived" data.

-- Martin Sperl

git-svn-id: svn://svn.oetiker.ch/rrdtool/trunk/program@1678 a5681a0c-68f1-0310-ab6d-d61299d08faa