Update documentation/InitDb to use musicbrainz_unaccent extension
Update README to require Pg 9.1
Hyperlink INSTALL.md from README.md

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Require Pg 9.1 before doing any work in InitDb.pl
Install musicbrainz_collate as an extension
Remove PostgreSQL < 9.1 support from script/create_test_db.sh
Reintroduce CreateSearchConfiguration.sql to create the mb_simple search configuration
Fix script/create_test_db.sh to recreate extensions
Merge branch 'unaccent-extension'