opentxs-notary crash if port is already in use

[mhamrle]

you can reproduce this issue by:
opentxs-notary &
rm ~/.ot/server_data/ot.pid
opentxs-notary

output:

** Main Server Contract Verified **
Listen: Exception Caught: Address already in use

OT_ASSERT in /home/martin/git/opentxs/src/ext/Socket_ZMQ4.cpp at line 346
stack trace:
/home/martin/opentxs/lib/x86_64-linux-gnu/libopentxs-core.so.0 : opentxs::OTLog::logAssert(char const_, unsigned long, char const_)+0x134
/home/martin/opentxs/lib/x86_64-linux-gnu/libopentxs-core.so.0 : Assert::doAssert(char const_, unsigned long, char const_)+0x46
/home/martin/opentxs/lib/x86_64-linux-gnu/libopentxs-ext.so.0 : opentxs::OTSocket_ZMQ_4::Listen()+0x1f2
/home/martin/opentxs/lib/x86_64-linux-gnu/libopentxs-ext.so.0 : opentxs::OTSocket_ZMQ_4::Listen(opentxs::OTString const&)+0xfb
/home/martin/opentxs/lib/x86_64-linux-gnu/libopentxs-server.so.0 : opentxs::MessageProcessor::init(int)+0x207
/home/martin/opentxs/lib/x86_64-linux-gnu/libopentxs-server.so.0 : opentxs::MessageProcessor::MessageProcessor(opentxs::ServerLoader&)+0x50
/home/martin/opentxs/bin/opentxs-notary : main()+0x125
/lib/x86_64-linux-gnu/libc.so.6 : __libc_start_main()+0xf5
/home/martin/opentxs/bin/opentxs-notary() [0x4015cf]
ot_terminate: ot_terminate caught unhandled exception. type: N3zmq7error_tE what(): Address already in use
stack trace:
/home/martin/opentxs/lib/x86_64-linux-gnu/libopentxs-core.so.0 : opentxs::ot_terminate()+0x64
/usr/lib/x86_64-linux-gnu/libstdc++.so.6 : ()+0x5e836
/usr/lib/x86_64-linux-gnu/libstdc++.so.6 : ()+0x5e863
/home/martin/opentxs/lib/x86_64-linux-gnu/libopentxs-ext.so.0 : opentxs::OTSocket_ZMQ_4::Listen()+0x1f7
/home/martin/opentxs/lib/x86_64-linux-gnu/libopentxs-ext.so.0 : opentxs::OTSocket_ZMQ_4::Listen(opentxs::OTString const&)+0xfb
/home/martin/opentxs/lib/x86_64-linux-gnu/libopentxs-server.so.0 : opentxs::MessageProcessor::init(int)+0x207
/home/martin/opentxs/lib/x86_64-linux-gnu/libopentxs-server.so.0 : opentxs::MessageProcessor::MessageProcessor(opentxs::ServerLoader&)+0x50
/home/martin/opentxs/bin/opentxs-notary : main()+0x125
/lib/x86_64-linux-gnu/libc.so.6 : __libc_start_main()+0xf5
/home/martin/opentxs/bin/opentxs-notary() [0x4015cf]
Aborted (core dumped)