Update: I got a TP-Link TL-WDN3200 for my Raspberry. My previous post still applies
for this dongle. You can skip the part where you need to compile your own hostapd, and go for the default one.
Same script, only hostapd driver should be 'nl80211' instead of 'rtl871xdrv'.
I also upgraded to the latest Raspbian (2014-09-24). I got some problems with /etc/network/interfaces. Mysteriously a wlan1 was configured there. When I commented out everything with wlan1, everything worked again.
