code: def is_installed(self, shutit_module_obj):
  		
  		shutit_global.shutit_global_object.yield_to_draw()
  		# Cache first
  		if shutit_module_obj.module_id in self.get_current_shutit_pexpect_session_environment().modules_installed:
  			return True
  		if shutit_module_obj.module_id in self.get_current_shutit_pexpect_session_environment().modules_not_installed:
  			return False
  		# Is it installed?
  		if shutit_module_obj.is_installed(self):
  			self.get_current_shutit_pexpect_session_environment().modules_installed.append(shutit_module_obj.module_id)
  			return True
  		# If not installed, and not in cache, add it.
  		else:
  			if shutit_module_obj.module_id not in self.get_current_shutit_pexpect_session_environment().modules_not_installed:
  				self.get_current_shutit_pexpect_session_environment().modules_not_installed.append(shutit_module_obj.module_id)
  			return False
  		return False
docs: Returns true if this module is installed.
  		Uses cache where possible.