gSoC - ADD MERGE COMMAND - code patch submission

Dear All,

This is ZHAI BOXUAN, a student of gSoC 2010. My project is to add merge
command in postgres.

This is the first submission of our codes, which has finished the parser,
analyzer and rewriter parts.

If you are interested in this project, please download the source code in
attachment and have test.

There are 3 files in the attachement. Two .patch file is created on the
/src/backend and /src/include folders (between orignial psql 8.4.3 and our
modified edition).

There is a more detailed instruction in readme.

Any comments will be highly appreciated.

Thanks!