Add fix for old vims
Add fix for old vims

Old vim versions did not support both unicode() and str() in python2 bindings in 
a number of places.

Fixes #829
russellb/powerline,firebitsbr/powerline,magus424/powerline,Liangjianghao/powerline,dragon788/powerline,xxxhycl2010/powerline,Liangjianghao/powerline,dragon788/powerline,cyrixhero/powerline,s0undt3ch/powerline,kenrachynski/powerline,cyrixhero/powerline,junix/powerline,EricSB/powerline,seanfisk/powerline,bezhermoso/powerline,Luffin/powerline,IvanAli/powerline,keelerm84/powerline,lukw00/powerline,kenrachynski/powerline,seanfisk/powerline,DoctorJellyface/powerline,IvanAli/powerline,bartvm/powerline,QuLogic/powerline,darac/powerline,firebitsbr/powerline,EricSB/powerline,lukw00/powerline,blindFS/powerline,xfumihiro/powerline,DoctorJellyface/powerline,wfscheper/powerline,areteix/powerline,prvnkumar/powerline,darac/powerline,Luffin/powerline,seanfisk/powerline,areteix/powerline,dragon788/powerline,lukw00/powerline,IvanAli/powerline,junix/powerline,s0undt3ch/powerline,magus424/powerline,QuLogic/powerline,russellb/powerline,darac/powerline,junix/powerline,xxxhycl2010/powerline,xxxhycl2010/powerline,xfumihiro/powerline,QuLogic/powerline,firebitsbr/powerline,s0undt3ch/powerline,xfumihiro/powerline,magus424/powerline,wfscheper/powerline,S0lll0s/powerline,Luffin/powerline,russellb/powerline,prvnkumar/powerline,wfscheper/powerline,kenrachynski/powerline,EricSB/powerline,blindFS/powerline,keelerm84/powerline,S0lll0s/powerline,bartvm/powerline,bartvm/powerline,blindFS/powerline,bezhermoso/powerline,S0lll0s/powerline,Liangjianghao/powerline,cyrixhero/powerline,DoctorJellyface/powerline,bezhermoso/powerline,prvnkumar/powerline,areteix/powerline