[collectd] configure option --with-rrdtool

[cydvd at autistici.org]

Hallo,
thanks to Florian for the documentation about the inclusion of a new 
plugin into the source tree; i'm actually trying to write the named 
plugin.

I've another little problem in the compile process from sources; all 
compiles perfectly, except for the rrdtool support.
I've correctly installed rrdtool 1.2.11 from sources, i've tried to 
specify the configure option "--with-rrdtool=<PATH>" in various way, 
specifing the path of the rrdtool sources, the path of the installed 
library librrdtool, or the path of the rrtool binaries. In all af those 
cases the configure process ends with a (librrd not found), with the 
result of the lost creation of the RRDs files during the collecting 
process after finishing make process.

Thanks, David