#32 reduce namespace pollution

[Jiri Baum]

The MatPLC library currently polutes the namespace
something shocking. We should reduce that, perhaps by
using the libtool -export-symbols or
-export-symbols-regex switches.

Note: currently, -export-symbols-regex reduces the
number of symbols reported by nm, but doesn't actually
eliminate them! We'll have to either wait for it to
start working correctly, or mess around with a version
script.

[Jiri Baum]

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Mostly done - see lib/plc.symbols

A few symbols in that file should really be cleaned up, in
particular sin_init_addr and bind_socket, and possibly also
the string_str_to_* ones.