update Rakefile, now only user in lrun group can run lrun directly.

* cache pkg-config results
* complain required binaries missing
* create 'lrun' group add install as -m2555 instead of -m4555
* change cxx flags to -std=c++11 from -std=c++0x
* update README to reflect changes
bump to 0.9.4.4
update README
Merge pull request #9 from quark-zju/development

Create lrun group for running lrun