pgsql: Rearrange yes/no prompting code so that the prompts always show

Log Message:
-----------
Rearrange yes/no prompting code so that the prompts always show the
(possibly (un)translated) letters that are actually expected as input.
Also reject invalid responses instead of silenty taken them as "no".

with help from Bernd Helmle

Modified Files:
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pgsql/src/bin/scripts:
common.c (r1.20 -> r1.21)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/scripts/common.c.diff?r1=1.20&r2=1.21)
common.h (r1.14 -> r1.15)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/scripts/common.h.diff?r1=1.14&r2=1.15)
createuser.c (r1.32 -> r1.33)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/scripts/createuser.c.diff?r1=1.32&r2=1.33)
dropdb.c (r1.17 -> r1.18)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/scripts/dropdb.c.diff?r1=1.17&r2=1.18)
dropuser.c (r1.18 -> r1.19)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/scripts/dropuser.c.diff?r1=1.18&r2=1.19)
nls.mk (r1.19 -> r1.20)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/scripts/nls.mk.diff?r1=1.19&r2=1.20)