Truncate names which are too long

Truncate names which are too long

When any name turned out too long, we returned "<pci_lookup_name: buffer too small>",
which wasn't very useful. Instead of that, we truncate the name and
we add "..." at the end.

Please note that for simplicity, the truncation happens only on systems with proper
C99 snprintf(). Ancient systems where snprintf() returns a negative number and
promises nothing about the state of the buffer still use the error message.