added ``app->env->has host`` to determine if ``host_exec`` can be used
added ``app->env->has host`` to determine if ``host_exec`` can be used

sedouard/TouchDevelop,UIKit0/TouchDevelop,jmptrader/TouchDevelop,jle33/TouchDevelop,Aksoom-Hussain/TouchDevelop,sedouard/TouchDevelop,SoftwareEngineeringToolDemos/FSE-2012-TouchDevelop,MetSystem/TouchDevelop,CodeKingdomsTeam/TouchDevelop,imadityab/FSE-2012-TouchDevelop-old,SoftwareEngineeringToolDemos/FSE-2012-TouchDevelop,imadityab/FSE-2012-TouchDevelop-old,imadityab/FSE-2012-TouchDevelop-old,CodeKingdomsTeam/TouchDevelop,CodeKingdomsTeam/TouchDevelop,sedouard/TouchDevelop,ntoll/TouchDevelop,UIKit0/TouchDevelop,SoftwareEngineeringToolDemos/FSE-2012-TouchDevelop,UIKit0/TouchDevelop,ntoll/TouchDevelop,imadityab/FSE-2012-TouchDevelop-old,jmptrader/TouchDevelop,SoftwareEngineeringToolDemos/FSE-2012-TouchDevelop,MetSystem/TouchDevelop,jle33/TouchDevelop,jle33/TouchDevelop,jmptrader/TouchDevelop,CodeKingdomsTeam/TouchDevelop,jmptrader/TouchDevelop,ntoll/TouchDevelop,jle33/TouchDevelop,SoftwareEngineeringToolDemos/FSE-2012-TouchDevelop,MetSystem/TouchDevelop,Aksoom-Hussain/TouchDevelop,jle33/TouchDevelop,Aksoom-Hussain/TouchDevelop,SoftwareEngineeringToolDemos/FSE-2012-TouchDevelop,SoftwareEngineeringToolDemos/FSE-2012-TouchDevelop