Started merging the code bases of Hai and Woo
Added basic structures

* Use S4 for class definitions

* Finished Database access layer

* In the database access layer, only the necessary functions are
  implemented

* db.writeTable needs special care because "distributed by" of GPDB
Use better file names
Added manual files, and make the package compilable
Added port in db.connect

Also let distributed.by == "" be the signature for randomly distributed
table in db.writeTable
Minor changes to improve usability
Tested the current db connection functions

* Removed unnecessary argument checks in the internal functions, and
  only keep argument checks for functions that are exposed to the users

* Various minor changes to improve the usability

* Added fetch function

* Corrected various small bugs

* Added .db.str2vec function
Better return values for db.connect and db.disconnect

* db.connect returns connection ID

* db.disconnect returns TRUE/FALSE
Start implementing db.data.frame
Moved .db.str2vec into utilities-generic.R
Added db.data.frame methods

Improved the doc for methods

Also added classes and export them
Added manual for classes

Also improved the name of the classes
Added dim and names methods for db.data.frame

The package is fully compilable now
Added content function and its manual

Adjusted member fields of the classes
Fixed a bug where multiple connections cannot be correctly handled

Also changed db.data.frame from method to normal function, just like the
function data.frame(...)
Added conn.id and its replacement function
Added print and show for db.data.frame

Also fixed a bug in .db.obj.info, where temporary schema was not handled
correcly
Pass MADlib schema name to the db.connect function
No need to install RPostgreSQL frin source
as.db.data.frame and better handling of TEMP objects

as.db.data.frame for db.data.frame is added. row.names is used as id.col
by default.

Better handling of TEMP objects and table/view names

.db.obj.info is obsolete! Do no use it anymore, but keep it in the
source code. Might be useful later

.db.existsTable/.db.existsTempTable do not work with view. Only
.is.table.or.view works for both table and view.