pgsql: Add PGTYPESchar_free() to avoid cross-module problems on Windows

Add PGTYPESchar_free() to avoid cross-module problems on Windows.

On Windows, it is sometimes important for corresponding malloc() and
free() calls to be made from the same DLL, since some build options can
result in multiple allocators being active at the same time. For that
reason we already provided PQfreemem(). This commit adds a similar
function for freeing string results allocated by the pgtypes library.

Author: Takayuki Tsunakawa
Reviewed-by: Kyotaro Horiguchi
Discussion: https://postgr.es/m/0A3221C70F24FB45833433255569204D1F8AD5D6%40G01JPEXMBYT05

Branch
------
REL9_6_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/b5b973ef0ba736c7c002f0907014d3115471644e

Modified Files
--------------
doc/src/sgml/ecpg.sgml | 24 +++++--
src/interfaces/ecpg/include/Makefile | 2 +-
src/interfaces/ecpg/include/pgtypes.h | 17 +++++
src/interfaces/ecpg/include/pgtypes_date.h | 1 +
src/interfaces/ecpg/include/pgtypes_interval.h | 1 +
src/interfaces/ecpg/include/pgtypes_numeric.h | 2 +
src/interfaces/ecpg/include/pgtypes_timestamp.h | 1 +
src/interfaces/ecpg/pgtypeslib/common.c | 10 +++
src/interfaces/ecpg/pgtypeslib/exports.txt | 1 +
.../ecpg/test/expected/pgtypeslib-dt_test.c | 84 +++++++++++-----------
.../ecpg/test/expected/pgtypeslib-dt_test2.c | 12 ++--
.../ecpg/test/expected/pgtypeslib-num_test.c | 10 +--
.../ecpg/test/expected/pgtypeslib-num_test2.c | 26 +++----
.../ecpg/test/expected/preproc-outofscope.c | 2 +
src/interfaces/ecpg/test/expected/sql-sqlda.c | 4 +-
src/interfaces/ecpg/test/pgtypeslib/dt_test.pgc | 84 +++++++++++-----------
src/interfaces/ecpg/test/pgtypeslib/dt_test2.pgc | 12 ++--
src/interfaces/ecpg/test/pgtypeslib/num_test.pgc | 10 +--
src/interfaces/ecpg/test/pgtypeslib/num_test2.pgc | 26 +++----
src/interfaces/ecpg/test/sql/sqlda.pgc | 2 +-
20 files changed, 192 insertions(+), 139 deletions(-)