Support multiline prompt in tcsh
Support multiline prompt in tcsh

Notes:

- I had to launch script twice because tcsh does not actually support multiline
  prompt: it squashes everything into one line.
- Thus I had to add POWERLINE_TCSH_NO_ABOVE_PROMPT: running python twice is not
  nice for performance.
- Due to 1) tcsh shifting rprompt by 1 and 2) tcsh not accepting %{%}-escaped
  color section at the very end of rprompt (actually it is accepting it, just
  makes user input colored as that section) I had to reduce computed width by 2.
- As running powerline command in precmd modifies status code I had to use
  POWERLINE_STATUS variable to save status.
- As tcsh does not accept names that start with underscore non-API powerline
  variables do not start with underscore.

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