pgsql: Revive line type

Revive line type

Change the input/output format to {A,B,C}, to match the internal
representation.

Complete the implementations of line_in, line_out, line_recv, line_send.
Remove comments and error messages about the line type not being
implemented. Add regression tests for existing line operators and
functions.

Reviewed-by: rui hua <365507506hua(at)gmail(dot)com>
Reviewed-by: Álvaro Herrera <alvherre(at)2ndquadrant(dot)com>
Reviewed-by: Jeevan Chalke <jeevan(dot)chalke(at)enterprisedb(dot)com>

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/261c7d4b653bc3e44c31fd456d94f292caa50d8f

Modified Files
--------------
doc/src/sgml/datatype.sgml | 42 ++++-
doc/src/sgml/func.sgml | 6 +
src/backend/utils/adt/geo_ops.c | 224 ++++++++++-------------
src/include/catalog/pg_type.h | 3 +-
src/include/utils/geo_decls.h | 7 -
src/test/regress/expected/geometry.out | 3 -
src/test/regress/expected/line.out | 271 ++++++++++++++++++++++++++++
src/test/regress/expected/sanity_check.out | 3 +-
src/test/regress/output/misc.source | 3 +-
src/test/regress/parallel_schedule | 2 +-
src/test/regress/serial_schedule | 1 +
src/test/regress/sql/geometry.sql | 4 -
src/test/regress/sql/line.sql | 87 +++++++++
13 files changed, 503 insertions(+), 153 deletions(-)