Clear errno before calling strtod()
Clear errno before calling strtod()

Fixes GH-27.

akheron/jansson,npmccallum/jansson,attie/jansson,simonfojtu/FireSight,firepick1/jansson,firepick1/jansson,firepick1/FireSight,chrullrich/jansson,wirebirdlabs/featherweight-jansson,bstarynk/jansson,simonfojtu/FireSight,liu3tao/jansson,firepick1/FireSight,Mephistophiles/jansson,simonfojtu/FireSight,markalanj/jansson,firepick1/FireSight,yahoo/ygloo-external-jansson,gameclosure/jansson,attie/jansson,slackner/jansson,wirebirdlabs/featherweight-jansson,firepick-delta/FireSight,akheron/jansson,bstarynk/jansson,AmesianX/jansson,firepick-delta/FireSight,rogerz/jansson,Mephistophiles/jansson,markalanj/jansson,gameclosure/jansson,rogerz/jansson,npmccallum/jansson,rogerz/jansson,markalanj/jansson,bstarynk/jansson,firepick-delta/FireSight,OlehKulykov/jansson,yahoo/ygloo-external-jansson,OlehKulykov/jansson,liu3tao/jansson,slackner/jansson,chrullrich/jansson,akheron/jansson,gameclosure/jansson,yahoo/ygloo-external-jansson,rogerz/jansson,Vorne/jansson,AmesianX/jansson,yahoo/ygloo-external-jansson,Vorne/jansson,firepick1/jansson