Log Message:
rrdtool: updated to 1.7.2

RRDtool 1.7.2:

Bugfixes
* Updated the Makefiles to properly include all needed files into the \ 
distribution tar
* Cleand up Compiler Warnings
* Improved compilation in MinGW environment
* fix segfault on non-existent RRD file when using rrdcached
* fix bounds handling, documentation and checking on rrdtool xport
* Fix %s/%S unit autoscaling in gprint for json/xml
* Optimized PDP Calculation