Added a mutex to protect a critical region in Gtk2 where the list can be

Added a mutex to protect a critical region in Gtk2 where the list can be
modified while the draw thread is walking it.

Changed the cmdline switch to -z so the same one can be used both for
ethereal and tethereal.

Updated man pages to reflect the RPCSTAT feature.

(Try this with Tools/Statistics/ONC-RPC/RTT and load a capture containing
onc-rpc. )

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@6189 f5534014-38df-0310-8fa8-9805f1628bb7