Fix make distcheck (releases master and 5.2)

Hello,

make distcheck does not work again (my previous fix was not enough).
2 problems :
- when you uninstall perl module. The paths may differ on the computer you build collectd on.
- libcollectdclient was updated and needs $top_srcdir/src/collectd.h

I had to create a small perl script that uninstall the module.

This patch was made against branch master but should probably work on 5.2 (no more on 5.1)

Regards,
Yves