Need some help with a query (uniq -c)

Hello!

I have a table (think of it as a table of log messages)

time | message
-----------------------
1 | a
2 | b
3 | b
4 | b
5 | a

the three 'b' are the same message, so I would like to write a query
that would give me a result that is similar to what the unix command
"uniq -c" would give:

first | message | last | count
--------------------------------------
1 | a | 1 | 1
2 | b | 4 | 3 <--- here it squeezes
similar consecutive messages into a single row
5 | a | 5 | 1

How do I write such a command?

I could of course write a plpgsql function that loops but that is not
as interesting as finding out if this can be done in a single simple
command.

Perhaps it would be best to regularly delete neighbouring similar
rows and keeping a "count" value would reduce the number of rows and
make it more efficient if the query would be run many times and the
number of duplicate messages would be large.