Code and docs review for multiple -c and -f options in psql.

Code and docs review for multiple -c and -f options in psql.

Commit d5563d7df94488bf drew complaints from Coverity, which quite
correctly complained that one copy of each -c or -f string was being
leaked.  What's more, simple_action_list_append was allocating enough space
for still a third copy of each string as part of the SimpleActionListCell,
even though that coding method had been superseded by a separate strdup
operation.  There were some other minor coding infelicities too.  The
documentation needed more work as well, eg it forgot to explain that -c
causes psql not to accept any interactive input.