ALEPPO — Um Khalid, a middle-aged mother of three, is not used to wearing a headscarf, let alone sneaking through military checkpoints. But instead of holding her breath, like the anti-government activists in the back seat of her car, she waved happily at the young soldier with the AK-47, who glared back at her through the windshield. She is driving the activists to Salahaddin, this city's most restive and dangerous neighborhood.