Adapt to relative path bug fix in purell
Adapt to relative path bug fix in purell

Temporary workaround for the bug fix and resulting
behavioral change in purell.NormalizeURLString():
a leading '/' was inadvertently to relative links,
but no longer, see #878.

I think the real solution is to allow Hugo to
make relative URL with relative path,
e.g. "../../post/hello-again/", as wished by users
in issues #157, #622, etc., without forcing
relative URLs to begin with '/'.
Once the fixes are in, let's remove this kludge
and restore SanitizeUrl() to the way it was.

Fixes #878

mitchchn/hugo,mdhender/hugo,MarkDBlackwell/hugo,ryanclarke/hugo,soundrussian/hugo,tatsushid/hugo,bogem/hugo,halostatue/hugo,fedelibre/hugo,derekperkins/hugo,badoet/hugo,Zenithar/hugo,bogem/hugo,badoet/hugo,digitalcraftsman/hugo,fedelibre/hugo,kujohn/hugo,gohugoio/hugo,sprig/hugo,tatsushid/hugo,Zenithar/hugo,fhergomez/hugo,bramp/hugo,mdhender/hugo,anthonyfok/hugo,soundrussian/hugo,bramp/hugo,ffrizzo/hugo,ryanclarke/hugo,mayah/hugo,coderzh/hugo,vbatoufflet/hugo,coderzh/hugo,derekperkins/hugo,digitalcraftsman/hugo,kujohn/hugo,abourget/hugo,ifraixedes/hugo,mayah/hugo,mitchchn/hugo,ffrizzo/hugo,sprig/hugo,tjyang/hugo,jygastaud/hugo,tubo028/hugo,mdhender/hugo,fhergomez/hugo,gohugoio/hugo,ifraixedes/hugo,mdhender/hugo,tischda/hugo,jygastaud/hugo,tischda/hugo,abourget/hugo,gohugoio/hugo,MarkDBlackwell/hugo,fedelibre/hugo,fedelibre/hugo,tubo028/hugo,melo/hugo,anthonyfok/hugo,tjyang/hugo,anthonyfok/hugo,vbatoufflet/hugo,melo/hugo,halostatue/hugo