message string fixes

Hi,

While translating the backend's message catalog I found several things
that should probably be improved.

For example, in regis.c there are several strings talking about "regis
pattern".  I had never heard of regis patterns.  Turns out they are a
fast regex subset, used AFAICT only by the ispell code.  Searching the
web I don't find any other reference to "regises" (regisen? reges?), so
I think we should avoid using the term.  How about just changing the
messages to just say "regular expression" instead?

Additionally, I would like to apply the attached patch.  Are there
objections?

--
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.