pgsql: Fix some bogus direct uses of realloc().

Fix some bogus direct uses of realloc().

pg_dump/parallel.c was using realloc() directly with no error check.
While the odds of an actual failure here seem pretty low, Coverity
complains about it, so fix by using pg_realloc() instead.

While looking for other instances, I noticed a couple of places in
psql that hadn't gotten the memo about the availability of pg_realloc.
These aren't bugs, since they did have error checks, but verbosely
inconsistent code is not a good thing.

Back-patch as far as 9.3. 9.2 did not have pg_dump/parallel.c, nor
did it have pg_realloc available in all frontend code.

Branch
------
REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/8824bae87b78036c41ba794d96a0e68859df5990

Modified Files
--------------
src/bin/pg_dump/parallel.c | 4 ++--
src/bin/psql/command.c | 7 +------
src/bin/psql/tab-complete.c | 9 ++-------
3 files changed, 5 insertions(+), 15 deletions(-)