Would help using adapt(unicode) to quote strings without a connection,
see ticket #331.

Currently in heisenbug state: if test_connection_wins_anyway and
test_encoding_default run (in this order), the latter fail because the
returned value is "'\xe8 '", with an extra space. Skipping the first
test, the second succeed.

The bad value is returned by the libpq:

    ql = PQescapeString(to+eq+1, from, len);

just returns len = 2 and an extra space in the string... meh.

These functions don't need to exist: exposing the type in the module is
enough. It is actually better as one may use isinstance and such.

Dropped encoding parameter in the constructor: it is used
nowhere and not documented. Use directly the connection
encoding if available, else the previous latin1 fallback.

This allows dropping repeated dictionary lookups with unicode
query/parameters.

.c files only need to import psycopg.h: it will in turn import
dependencies from Python and libpq and configure.h. psycopg.h should be
the first to be imported, so the basic imports are not required in
the .h's

As a guideline I'm trying to import from the most specific to the most
generic to detect missing imports in the .h's.

	that should not be exported from the module.  This results in a 5%
	reduction in code size and shortens the dynamic symbol table.

	* psycopg/config.h: If GCC >= 4.0 is installed, define the HIDDEN
	symbol to apply the "hidden" visibility attribute.