title: Problems with $libdir on PostgreSQL
body: <p>In short, my question is "why doesn't $libdir work on my PSQL installation."  </p>
  
  <pre><code>CREATE FUNCTION st_box2d_in(cstring) RETURNS box2d
      AS '$libdir/liblwgeom', 'BOX2DFLOAT4_in'
      LANGUAGE c IMMUTABLE STRICT;
  </code></pre>
  
  <p>yields an error</p>
  
  <pre><code>could not access file "$libdir/liblwgeom": No such file or directory
  </code></pre>
  
  <p>while</p>
  
  <pre><code>CREATE FUNCTION st_box2d_in(cstring) RETURNS box2d
      AS '/usr/local/pgsql/lib/liblwgeom', 'BOX2DFLOAT4_in'
      LANGUAGE c IMMUTABLE STRICT;
  </code></pre>
  
  <p>works correctly.</p>
  
  <p>The output of </p>
  
  <pre><code>% pg_config --pkglibdir
  /usr/local/pgsql/lib
  </code></pre>
  
  <p>appears to be correct.</p>