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.
* psycopg/config.h: only print debug messages if
psycopg_debug_enabled is true.
* psycopg/psycopgmodule.c (init_psycopg): set
psycopg_debug_enabled to true if the $PSYCOPG_DEBUG environment
variable is set.