pgpool: Fix pg_enc not working if both -p and -P are provided.

Fix pg_enc not working if both -p and -P are provided.

In the original report (https://github.com/pgpool/pgpool2/issues/129:

[root(at)test1 bin]# ./pg_enc -p -P
db password:
encryption key:
encryption key not provided

Also I found a misleading comment:
case 'p': /* prompt for postgres password */

This is not appropriate since the password is not provided to
PostgreSQL. It is totally unrelated to the issue but I replaced it
with following in this opportunity:

case 'p': /* prompt for password to be encrypted */

Author: jinyang liu <liujy(at)highgo(dot)com>
Discussion: https://www.postgresql.org/message-id/7f18c30b.237.1997555ca11.Coremail.liujy%40highgo.com
Backpatch-through: v4.2

Branch
------
V4_6_STABLE

Details
-------
https://git.postgresql.org/gitweb?p=pgpool2.git;a=commitdiff;h=59a359eef24c73e03c894eae7598949d396da178

Modified Files
--------------
src/tools/pgenc/pg_enc.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)