Don't fail if mercurial repository has no parent.
Don't fail if mercurial repository has no parent.

On behalf of: ced

Review URL: https://codereview.appspot.com/101710043/

sajingeo/rietveld,Koulio/rietveld,aungzanbaw/rietveld,ericmckean/rietveld,v3ss0n/rietveld,rietveld-codereview/rietveld,Koulio/rietveld,robfig/rietveld,gavioto/rietveld,supriyantomaftuh/rietveld,google-code-export/rietveld,Koulio/rietveld,dushmis/rietveld,andyzsf/rietveld,xtypebee/rietveld,berkus/rietveld,rietveld-codereview/rietveld,supriyantomaftuh/rietveld,salomon1184/rietveld,salomon1184/rietveld,google-code-export/rietveld,openlabs/cr.openlabs.co.in,google-code-export/rietveld,gavioto/rietveld,robfig/rietveld,aungzanbaw/rietveld,andyzsf/rietveld,dushmis/rietveld,draem0507/rietveld,ericmckean/rietveld,gavioto/rietveld,aungzanbaw/rietveld,fuzan/rietveld,supriyantomaftuh/rietveld,gco/rietveld,v3ss0n/rietveld,arg0/rietveld,arg0/rietveld,foolonhill/rietveld,berkus/rietveld,v3ss0n/rietveld,sajingeo/rietveld,DeanHere/rietveld,salomon1184/rietveld,xtypebee/rietveld,DeanHere/rietveld,xtypebee/rietveld,rietveld-codereview/rietveld,openlabs/cr.openlabs.co.in,foolonhill/rietveld,draem0507/rietveld,fuzan/rietveld,draem0507/rietveld,ericmckean/rietveld,sajingeo/rietveld,foolonhill/rietveld,fuzan/rietveld,DeanHere/rietveld,gco/rietveld,berkus/rietveld,dushmis/rietveld,openlabs/cr.openlabs.co.in,robfig/rietveld,gco/rietveld,andyzsf/rietveld,rietveld-codereview/rietveld,arg0/rietveld