Minor improvements for testing
Bug fix: The product of two arrays should also be an array

It is very possible that other operations for two db.obj objects
have the the same problem.
Removed the initial message about GUI
Allow db.array to work on an array column
Fixed the bug in merge that blocked adaboost
Allowed append for data.frame and file in as.db.data.frame
Updated the doc for append
Fixed bugs related to handling of special column names
Disabled -Wreturn-type-c-linkage warning
Bug fix: handle view correctly in the formula handling part
Better messages for as.db.data.frame
Bug fix: margins and vcov does not handle NULL properly

Now na.omit works
Automatic detect whether MADlib lm/glm skipped NULL

in margins and vcov
Bug fix: without intercept should be in model.matrix

for analyzing factors
Bug fix: array index cannot be larger than 10 in margins
Bug fix: margins did not deal with expression in dependent variable

After this fix, expression can be directly used as dependent variable in
regression and margins will not give error.
Bug fix: error for crossprod if the user does not have permission to /tmp

Avoid using /tmp
Allow variables appear in both dependent and independents
Bug fix for a doc example

primary keys must be a subset of distributed.by
Made - work for time types