pgsql: Improve regression tests for degree-based trigonometric function

Improve regression tests for degree-based trigonometric functions.

Print the actual value of each function result that's expected to be exact,
rather than merely emitting a NULL if it's not right. Although we print
these with extra_float_digits = 3, we should not trust that the platform
will produce a result visibly different from the expected value if it's off
only in the last place; hence, also include comparisons against the exact
values as before. This is a bit bulkier and uglier than the previous
printout, but it will provide more information and be easier to interpret
if there's a test failure.

Discussion: <18241(dot)1461073100(at)sss(dot)pgh(dot)pa(dot)us>

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/4db0d2d2fe935e086dfd26c00f707dab298b443c

Modified Files
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.../expected/float8-exp-three-digits-win32.out | 155 ++++++++++++---------
src/test/regress/expected/float8-small-is-zero.out | 155 ++++++++++++---------
.../regress/expected/float8-small-is-zero_1.out | 155 ++++++++++++---------
src/test/regress/expected/float8.out | 155 ++++++++++++---------
src/test/regress/sql/float8.sql | 48 +++++--
5 files changed, 399 insertions(+), 269 deletions(-)