Tests for spi/triggers

src/test/regress/GNUmakefile

src/test/regress/expected/triggers.out

src/test/regress/input/create_function_1.source

src/test/regress/output/create_function_1.source

src/test/regress/regress.c

src/test/regress/sql/tests

src/test/regress/sql/triggers.sql