Make sure arguments in `args` are only strings
Make sure arguments in `args` are only strings

Required for python-2.6

Fixes #933
Luffin/powerline,lukw00/powerline,cyrixhero/powerline,QuLogic/powerline,russellb/powerline,dragon788/powerline,xfumihiro/powerline,lukw00/powerline,QuLogic/powerline,wfscheper/powerline,Liangjianghao/powerline,prvnkumar/powerline,seanfisk/powerline,blindFS/powerline,s0undt3ch/powerline,junix/powerline,darac/powerline,DoctorJellyface/powerline,seanfisk/powerline,darac/powerline,bartvm/powerline,kenrachynski/powerline,IvanAli/powerline,bezhermoso/powerline,xfumihiro/powerline,bezhermoso/powerline,magus424/powerline,blindFS/powerline,s0undt3ch/powerline,firebitsbr/powerline,Liangjianghao/powerline,prvnkumar/powerline,Luffin/powerline,EricSB/powerline,junix/powerline,russellb/powerline,kenrachynski/powerline,DoctorJellyface/powerline,russellb/powerline,EricSB/powerline,s0undt3ch/powerline,Luffin/powerline,xfumihiro/powerline,junix/powerline,magus424/powerline,xxxhycl2010/powerline,bezhermoso/powerline,firebitsbr/powerline,wfscheper/powerline,areteix/powerline,dragon788/powerline,Liangjianghao/powerline,lukw00/powerline,magus424/powerline,cyrixhero/powerline,dragon788/powerline,xxxhycl2010/powerline,QuLogic/powerline,darac/powerline,bartvm/powerline,EricSB/powerline,wfscheper/powerline,bartvm/powerline,DoctorJellyface/powerline,IvanAli/powerline,cyrixhero/powerline,areteix/powerline,seanfisk/powerline,blindFS/powerline,S0lll0s/powerline,prvnkumar/powerline,kenrachynski/powerline,IvanAli/powerline,S0lll0s/powerline,firebitsbr/powerline,areteix/powerline,S0lll0s/powerline,xxxhycl2010/powerline