pgsql: Improve reporting of error situations in find_other_exec().

Improve reporting of error situations in find_other_exec().

This function suppressed any stderr output from the called program, which
is unnecessary in the normal case and unhelpful in error cases. It also
gave a rather opaque message along the lines of "fgets failure: Success"
in case the called program failed to return anything on stdout. Since
we've seen multiple reports of people not understanding what's wrong when
pg_ctl reports this, improve the message.

Back-patch to all active branches.

Branch
------
REL9_2_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/62d69045dd1c41bbcd8a7f78c7a4170e8381ca76

Modified Files
--------------
src/port/exec.c | 12 ++++++++++--
1 files changed, 10 insertions(+), 2 deletions(-)