pgsql: Clean up password prompting logic in streamutil.c.

Clean up password prompting logic in streamutil.c.

The previous coding was fairly unreadable and drew double-free warnings
from clang. I believe the double free was actually not reachable, because
PQconnectionNeedsPassword is coded to not return true if a password was
provided, so that the loop can't iterate more than twice. Nonetheless
it seems worth rewriting. No back-patch since this is just cosmetic.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/3172eea062e779db39df9a48fca0ad7448163f98

Modified Files
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src/bin/pg_basebackup/streamutil.c | 110 ++++++++++++++++++------------------
1 file changed, 56 insertions(+), 54 deletions(-)