Make sure that recompaction writes a pristine new depslog.
Make sure that recompaction writes a pristine new depslog.

...even if a prior run of DepsLog::Recompact() exited without cleaning
up, for example due to a crash or because someone added a `return true;`
in the middle of the function while debugging.  Or because someone hits
ctrl-c during deps log recompaction.

No test, because I can't think of a way to trigger this scenario
programmatically.

Part of issue #554.

vvvrrooomm/ninja,nocnokneo/ninja,ignatenkobrain/ninja,Qix-/ninja,yannicklm/ninja,colincross/ninja,mydongistiny/ninja,Qix-/ninja,fuchsia-mirror/third_party-ninja,lizh06/ninja,dorgonman/ninja,jimon/ninja,mgaunard/ninja,pathscale/ninja,ctiller/ninja,fuchsia-mirror/third_party-ninja,dendy/ninja,ndsol/subninja,nafest/ninja,yannicklm/ninja,drbo/ninja,autopulated/ninja,Ju2ender/ninja,nocnokneo/ninja,bmeurer/ninja,tfarina/ninja,guiquanz/ninja,TheOneRing/ninja,sxlin/dist_ninja,nicolasdespres/ninja,vvvrrooomm/ninja,martine/ninja,automeka/ninja,nocnokneo/ninja,bradking/ninja,jhanssen/ninja,colincross/ninja,sgraham/ninja,nafest/ninja,guiquanz/ninja,mdempsky/ninja,Maratyszcza/ninja-pypi,nafest/ninja,glensc/ninja,TheOneRing/ninja,tfarina/ninja,bmeurer/ninja,ilor/ninja,rnk/ninja,mydongistiny/ninja,synaptek/ninja,atetubou/ninja,purcell/ninja,hnney/ninja,juntalis/ninja,sgraham/ninja,moroten/ninja,sxlin/dist_ninja,synaptek/ninja,metti/ninja,pathscale/ninja,ignatenkobrain/ninja,jhanssen/ninja,rnk/ninja,juntalis/ninja,dpwright/ninja,ilor/ninja,mydongistiny/ninja,glensc/ninja,AoD314/ninja,kimgr/ninja,jendrikillner/ninja,kimgr/ninja,mgaunard/ninja,ThiagoGarciaAlves/ninja,kissthink/ninja,jendrikillner/ninja,yannicklm/ninja,Ju2ender/ninja,colincross/ninja,iwadon/ninja,syntheticpp/ninja,purcell/ninja,rjogrady/ninja,fuchsia-mirror/third_party-ninja,purcell/ninja,juntalis/ninja,ndsol/subninja,nico/ninja,dendy/ninja,kimgr/ninja,mohamed/ninja,sgraham/ninja,sorbits/ninja,sorbits/ninja,TheOneRing/ninja,nico/ninja,sxlin/dist_ninja,atetubou/ninja,sxlin/dist_ninja,glensc/ninja,jimon/ninja,fifoforlifo/ninja,hnney/ninja,moroten/ninja,dorgonman/ninja,purcell/ninja,ignatenkobrain/ninja,bradking/ninja,lizh06/ninja,autopulated/ninja,syntheticpp/ninja,metti/ninja,maruel/ninja,automeka/ninja,ctiller/ninja,autopulated/ninja,bmeurer/ninja,metti/ninja,sorbits/ninja,glensc/ninja,Maratyszcza/ninja-pypi,martine/ninja,rnk/ninja,jhanssen/ninja,hnney/ninja,iwadon/ninja,nicolasdespres/ninja,juntalis/ninja,dorgonman/ninja,ThiagoGarciaAlves/ninja,lizh06/ninja,automeka/ninja,martine/ninja,Ju2ender/ninja,metti/ninja,rjogrady/ninja,mdempsky/ninja,dorgonman/ninja,lizh06/ninja,dendy/ninja,nicolasdespres/ninja,drbo/ninja,dpwright/ninja,kimgr/ninja,atetubou/ninja,AoD314/ninja,yannicklm/ninja,ilor/ninja,jimon/ninja,tfarina/ninja,mohamed/ninja,colincross/ninja,drbo/ninja,dpwright/ninja,Maratyszcza/ninja-pypi,fifoforlifo/ninja,tfarina/ninja,autopulated/ninja,jendrikillner/ninja,ninja-build/ninja,martine/ninja,nico/ninja,liukd/ninja,maruel/ninja,mohamed/ninja,drbo/ninja,Qix-/ninja,liukd/ninja,ndsol/subninja,bmeurer/ninja,ThiagoGarciaAlves/ninja,ninja-build/ninja,vvvrrooomm/ninja,vvvrrooomm/ninja,nafest/ninja,nickhutchinson/ninja,guiquanz/ninja,iwadon/ninja,fuchsia-mirror/third_party-ninja,mdempsky/ninja,ninja-build/ninja,bradking/ninja,sxlin/dist_ninja,ndsol/subninja,nickhutchinson/ninja,ilor/ninja,ninja-build/ninja,moroten/ninja,kissthink/ninja,synaptek/ninja,sorbits/ninja,liukd/ninja,ThiagoGarciaAlves/ninja,pathscale/ninja,bradking/ninja,nocnokneo/ninja,mohamed/ninja,mgaunard/ninja,rjogrady/ninja,rnk/ninja,jendrikillner/ninja,rjogrady/ninja,nickhutchinson/ninja,AoD314/ninja,AoD314/ninja,ctiller/ninja,atetubou/ninja,kissthink/ninja,nico/ninja,moroten/ninja,kissthink/ninja,ignatenkobrain/ninja,sxlin/dist_ninja,iwadon/ninja,pathscale/ninja,maruel/ninja,dpwright/ninja,jimon/ninja,fifoforlifo/ninja,ctiller/ninja,guiquanz/ninja,mgaunard/ninja,Maratyszcza/ninja-pypi,dendy/ninja,jhanssen/ninja,mydongistiny/ninja,sgraham/ninja,automeka/ninja,nickhutchinson/ninja,mdempsky/ninja,maruel/ninja,Ju2ender/ninja,liukd/ninja,sxlin/dist_ninja,nicolasdespres/ninja,syntheticpp/ninja,fifoforlifo/ninja,hnney/ninja,Qix-/ninja,synaptek/ninja,syntheticpp/ninja,TheOneRing/ninja