Problem: undocumented limit on IPC paths in Linux is 107 chars

Solution: document the limit of 113 chars including ipc://. We might
fix this in libzmq by shortening an over-long IPC pathname into a
unique string; so long as this is done consistently in bind and in
connect, it will save applications from weird failures when they
use external data to generate IPC pathnames.
Merge pull request #1176 from hintjens/master

Problem: undocumented limit on IPC paths in Linux is 107 chars