Windows: Use posixpath in nav.FC.make_absolute()
Windows: Use posixpath in nav.FC.make_absolute()

nav.FileContext.make_absolute() is only used to compare
links to entries in mkdocs.yml, so it makes sense for it
to only use POSIX-style paths.

Without this, the site fails to build because it checks for
a Windows-style path in a list of POSIX paths in
build.PathToURL.__call__().

This is the last change required to build the mkdocs site
on Windows.

jpush/mkdocs,cnbin/mkdocs,justinkinney/mkdocs,waylan/mkdocs,simonfork/mkdocs,samuelcolvin/mkdocs,lbenet/mkdocs,rickpeters/mkdocs,gregelin/mkdocs,xeechou/mkblogs,jamesbeebop/mkdocs,nicoddemus/mkdocs,xeechou/mkblogs,samhatfield/mkdocs,ericholscher/mkdocs,jamesbeebop/mkdocs,tedmiston/mkdocs,tedmiston/mkdocs,lukfor/mkdocs,mlzummo/mkdocs,justinkinney/mkdocs,mlzummo/mkdocs,dmehra/mkdocs,jeoygin/mkdocs,lbenet/mkdocs,mkdocs/mkdocs,cnbin/mkdocs,samuelcolvin/mkdocs,d0ugal/mkdocs,michaelmcandrew/mkdocs,ramramps/mkdocs,wenqiuhua/mkdocs,longjl/mkdocs,pjbull/mkdocs,rickpeters/mkdocs,vi4m/mkdocs,fujita-shintaro/mkdocs,jamesbeebop/mkdocs,peter1000/mkdocs,vi4m/mkdocs,vi4m/mkdocs,kubikusrubikus/mkdocs,cazzerson/mkdocs,wenqiuhua/mkdocs,justinkinney/mkdocs,peter1000/mkdocs,rickpeters/mkdocs,longjl/mkdocs,dmehra/mkdocs,jeoygin/mkdocs,mkdocs/mkdocs,xeechou/mkblogs,simonfork/mkdocs,samuelcolvin/mkdocs,ericholscher/mkdocs,williamjmorenor/mkdocs,jpush/mkdocs,mkdocs/mkdocs,tedmiston/mkdocs,waylan/mkdocs,cazzerson/mkdocs,kubikusrubikus/mkdocs,d0ugal/mkdocs,samhatfield/mkdocs,williamjmorenor/mkdocs,dmehra/mkdocs,michaelmcandrew/mkdocs,peter1000/mkdocs,ramramps/mkdocs,jpush/mkdocs,davidgillies/mkdocs,davidgillies/mkdocs,fujita-shintaro/mkdocs,lbenet/mkdocs,jimporter/mkdocs,gregelin/mkdocs,hhg2288/mkdocs,nicoddemus/mkdocs,waylan/mkdocs,davidgillies/mkdocs,gregelin/mkdocs,michaelmcandrew/mkdocs,longjl/mkdocs,cazzerson/mkdocs,jeoygin/mkdocs,wenqiuhua/mkdocs,simonfork/mkdocs,jimporter/mkdocs,lukfor/mkdocs,pjbull/mkdocs,nicoddemus/mkdocs,fujita-shintaro/mkdocs,samhatfield/mkdocs,hhg2288/mkdocs,hhg2288/mkdocs,ramramps/mkdocs,jimporter/mkdocs,cazzerson/mkdocs,lukfor/mkdocs,d0ugal/mkdocs,mlzummo/mkdocs,pjbull/mkdocs,kubikusrubikus/mkdocs,cnbin/mkdocs,williamjmorenor/mkdocs,xeechou/mkblogs,wenqiuhua/mkdocs,ericholscher/mkdocs,jpush/mkdocs