Cleanup for gettext() calls

Our current use of gettext() calls is inconsistent. We use:

#define _(x) gettext((x))

in various C files to abreviate the use of gettext() around all string.
This patch makes that consistent by moving the define to include/c.h.

It also adds some missing gettext usage, particularly in src/port and
interfaces/ecpg.

I found that perl also defines _(x) so I undefined this in plperl. I
don't see c.h is externally used so it seems safe to just use it
consistently in our code.

The attached patch makes these adjustments.

Also, what is gettext_noop(x) used for? It seems it is just used to
mark strings that should not be translated, but why are certain strings
not to be translated?

--
Bruce Momjian | http://candle.pha.pa.us
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