Make it work for tables with "id" column

SQLite aliases "rowid" to "id" automatically if there is
an autoincrementing column "id". It also changes the label
by default to "id", confusing our code. If you do
"rowid as rowid" in the select, this forces the label we expect.

Should fix https://github.com/scraperwiki/odata-cgi/issues/5
Merge pull request #8 from scraperwiki/rowid-as-rowid

Make it work for tables with "id" column