BUG #6343: PGTYPES library missing qualifiers

The following bug has been logged on the website:

Bug reference:      6343
Logged by:          Daniel Loffgren
Email address:      kojiro@hello-channel.com
PostgreSQL version: 9.1.1
Operating system:   NetBSD
Description:=20=20=20=20=20=20=20=20

In the ecpg PGTYPES library, there are functions like this:=20

extern int PGTYPEStimestamp_fmt_asc(timestamp *, char *, int, char *);

The last argument is the formatting string, yet isn't constant. This
generates warnings/errors on many compilers that are watching for discarding
of qualifiers when passing in string literals. It's a simple fix, although I
noticed that in PGTYPEStimestamp_defmt_asc the code is altering the
formatter if it is null, which prevents making the formatter const. However,
dttofmtasc_replace does not alter the formatter, and so should not pose a
problem for PGTYPEStimestamp_fmt_asc which passes straight to it.