Update french translation of the 7.4 branch

Hi,

Here are some updates of the french .po files.

## pg_dump-fr.po
391 messages traduits.
## pg_resetxlog-fr.po
57 messages traduits.
## pgscripts-fr.po
112 messages traduits.
## psql-fr.po
455 messages traduits.

pg_resetxlog, pg_dump and pgscripts .po files are new ones.

They need to be apply with the 7.4 branch. Thanks.


--
Guillaume.
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