Greatly improve crossprod

Use new SQL functions to help improve the performance

Verified on DCA.

Also fixed a bug in delete (temporary tables cannot be deleted through
delete,db.data.frame-method)
Improved sample with replacement, also fixed a bug

bug: forgot to add sort$str in as.db.data.frame,db.Rquery-method
Minor changes caused by the previous commit
Improved error messages, fixed a bug

Made generic.cv and genric.bagging work again
Corrected a tiny bug for Postgres
Made PivotalR compatible with R-2.14.2

R-2.14.2 does not support the latest DBI, so I have to include DBI
source into inst and install it when needed.
Update README.md
Minor change to remove ... in cbind2 manual
Made compatible with 2.11 and newer
Made with work with all db.obj objects
Solved more compatibility issues with older versions of R

2.12, 2.13 do not have regmatches

2.11 does not have list2env and as.environment is not generic, has to
abandon it. Other workaround?
Fixed a small bug in db.connect
Minor changes to make it compatible with HAWQ
Bump the version to 0.1.7
Fixed a bug: Lookat cannot work with unique
If either dimension of preview result is 1, use drop=TRUE