Add single row mode of PostgreSQL 9.2

--HG--
branch : single_row_mode
Merged in larskanis/ruby-pg/single_row_mode (pull request #13: Add single row mode of PostgreSQL 9.2)
Add some more documentation to Connection#set_single_row_mode
Improve spec for Connection#set_single_row_mode
Use proper const check instead of implicit relation
Fix encoding of messages delivered by notice callbacks
Fix text encoding for Connection#wait_for_notify
Fix text encoding for Connection#notifies
Update PostgreSQL to 9.2.2 for cross compilation task
Merge http://github.com/ged/ruby-pg
Avoid warning about deprecated expect{ }.should.
Async connection test seems to be a bit racy on 1.8.7. So allow CONNECTION_OK, too.
Replace Encoding::KOI8_U by Encoding::KOI8_R to allow testing with PostgreSQL 8.3.
Skip some tests that do not run on PostgreSQL<9.0
Adjust PGError test to also match PostgreSQL 8.3
Don't do parameter test with 'keepalives' on PostgreSQL<9.0
Remove duplicated test.

It is equally defined in result_spec.rb.