fix a bug in PluginInterface
small change in GreedyHeuristic
small update in GreedyHeuristic
update default options
really failing if clasp configuration failed

(error is not in exception because throwing out of constructor
is unsafe (and might prevent the error to be displayed))
Merge branch 'master' into ps
making stats dumping a general feature (it can be useful)
added heuristics to defer propagation from clasp to HEX

currently configurable by options in ProgramCtx, will add commandline options when necessary
fixing wrong assertion and added comment why this is good
again setting submodule to newest version of dlvhex-common

(this time i did not even find the commit which reset it)