Makefile: 'make uninstall' will no longer purge any configuration files, added...

Makefile: 'make uninstall' will no longer purge any configuration files, added 'purge' target that also removes config files


git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@1229 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534