pgsql: ecpg: Move function prototype into header file

ecpg: Move function prototype into header file

PGTYPEStimestamp_defmt_scan() was declared twice inside different .c
files, with slightly different prototypes.  Move it into a header file
and correct the prototype.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/9feeef92fb9b73371e3f299ba444f86b4ef7e26f

Modified Files
--------------
src/interfaces/ecpg/pgtypeslib/dt.h        |    4 ++++
src/interfaces/ecpg/pgtypeslib/dt_common.c |    3 ---
src/interfaces/ecpg/pgtypeslib/timestamp.c |    3 ---
3 files changed, 4 insertions(+), 6 deletions(-)