description of translate()

Hi all,

I noticed that the existing description of the string translate()
function <http://www.postgresql.org/docs/current/static/functions-string.html#FUNCTIONS-STRING-OTHER>
currently has a description of:

Any character in string that matches a character in the from set is
replaced by the corresponding character in the to set

This description leaves off the other half of translate()'s
capability, namely stripping unwanted characters entirely. The comment
for the translate() in oracle_compat.c is helpful here, saying:

If from is longer than to, occurrences of the extra characters in
from are deleted.

Attached is a patch to update the doc page based on this comment's wording.

Josh