mkdir_p: account for '//foo/bar'
mkdir_p: account for '//foo/bar'

As Richard reported, dirname('//') returns //.  But mkdir_p only stops
when called with '/', resulting in infinite recursion when given a
pathname '//foo/bar'.

Reported-by: richard -rw- weinberger <a27366f0c35e42b402be5a128349bd1963d6dd0d@gmail.com>
Signed-off-by: Serge Hallyn <3df611b026e4639bee8aef7a4beb2e39fcebb313@ubuntu.com>

bostjan/lxc,JohnPeacockMessageSystems/lxc,hkjolhede/lxc,ioops/lxc,ksperis/lxc,hallyn/lxc,codebauss/lxc,abstrakraft/lxc-android-lxc,sapun/lxc,regit/lxc,ysbnim/lxc,hkjolhede/lxc,federicobriata/lxc,weizhenwei/lxc,armcc/lxc,lisongmin/lxc,bostjan/lxc,virajs/lxc,hfuCN/lxc,Distrotech/lxc,LynxChaus/lxc,sapun/lxc,ss1h2a3tw/lxc,rldleblanc/lxc,yubo/lxc,terceiro/lxc,lazy404/lxc,GreatFruitOmsk/lxc,Distrotech/lxc,weizhenwei/lxc,DarknessBeforeDawn/lxc,Ponce/lxc,ojkastl/lxc_Patches,tych0/lxc,akshaykarle/lxc,federicobriata/lxc,raspberrypython/lxc,QingweiPeterLan/cs188-lxc,yubo/lxc,DarknessBeforeDawn/lxc,rowhit/lxc,major/lxc,raspberrypython/lxc,lisongmin/lxc,thmo/lxc,major/lxc,smoser/lxc,LynxChaus/lxc,Ponce/lxc,raspberrypython/lxc,virajs/lxc,christiaan/lxc,glensc/lxc,ss1h2a3tw/lxc,regit/lxc,thmo/lxc,Pelagicore/lxc,rowhit/lxc,Pelagicore/lxc,federicobriata/lxc,yubo/lxc,codebauss/lxc,ss1h2a3tw/lxc,DarknessBeforeDawn/lxc,fwilson42/lxc,glensc/lxc,caglar10ur/lxc,smoser/lxc,QingweiPeterLan/cs188-lxc,glensc/lxc,sapun/lxc,jirislaby/lxc,GreatFruitOmsk/lxc,abstrakraft/lxc-android-lxc,fwilson42/lxc,terceiro/lxc,Ponce/lxc,bmoar/lxc,hfuCN/lxc,LynxChaus/lxc,cjwatson/lxc,Distrotech/lxc,caglar10ur/lxc,smoser/lxc,rowhit/lxc,abstrakraft/lxc-android-lxc,armcc/lxc,tych0/lxc,JohnPeacockMessageSystems/lxc,ysbnim/lxc,ojkastl/lxc_Patches,rldleblanc/lxc,lazy404/lxc,efiop/lxc,lisongmin/lxc,tych0/lxc,major/lxc,cjwatson/lxc,hallyn/lxc,abstrakraft/lxc-android-lxc,jirislaby/lxc,ecarrara/lxc,bostjan/lxc,armcc/lxc,efiop/lxc,ksperis/lxc,ojkastl/lxc_Patches,christiaan/lxc,aeris/lxc,terceiro/lxc,jirislaby/lxc,ecarrara/lxc,ksperis/lxc,ysbnim/lxc,akshaykarle/lxc,weizhenwei/lxc,szaszg/lxc,bmoar/lxc,christiaan/lxc,fwilson42/lxc,smoser/lxc,virajs/lxc,regit/lxc,ioops/lxc,thmo/lxc,szaszg/lxc,Pelagicore/lxc,GreatFruitOmsk/lxc,caglar10ur/lxc,lazy404/lxc,aeris/lxc,hallyn/lxc,aeris/lxc,szaszg/lxc,ojkastl/lxc_Patches,hkjolhede/lxc,ecarrara/lxc,rldleblanc/lxc,efiop/lxc,ioops/lxc,cjwatson/lxc,codebauss/lxc,hfuCN/lxc,JohnPeacockMessageSystems/lxc,QingweiPeterLan/cs188-lxc,akshaykarle/lxc,bmoar/lxc