Save IFS at startup to restore it in _lp_set_prompt
Save IFS at startup to restore it in _lp_set_prompt

We already restore IFS to its default value. This patch only changes the
way it is done to avoid a call to 'echo' in a sub-shell at runtime.
Fixes #267.

dtschan/liquidprompt,jonathanjsimon/liquidprompt,joshuarubin/dotfiles,timhyson/liquidprompt,dan-cleinmark/liquidprompt,tkuminecz/liquidprompt,joshuarubin/dotfiles,alexprengere/liquidprompt,pkkolos/liquidprompt,mathieumd/liquidprompt,colinlieberman/liquidprompt,smadhueagle/liquidprompt,illwieckz/liquidprompt,milouse/liquidprompt,BobHood/liquidprompt,jaesivsm/liquidprompt,dpilone/liquidprompt,joshuarubin/dotfiles,elementalvoid/liquidprompt,nojhan/liquidprompt,kenrachynski/liquidprompt,tstone2077/liquidprompt,laurentbardin/liquidprompt,joshuarubin/dotfiles,tocomo/liquidprompt,tsbarnes/liquidprompt,enrdstrm/liquidprompt,lyoshenka/liquidprompt