LDA: make get_perplexity faster
For older versions of GPDB, convert string to vectors before validation
of the arguments

This fixed the bug where data columns will be reported as missing.
Elastic Net regularization for linear models

FISTA and IGD optimizers are supported

Grouping support will be added later.
Elastic Net regularization for logistic models

Grouping support will be added later
Set use_active_set default to be false

Update user doc

Better help messages
LDA: Fix a bug introduced in Rev. 0fafa01
Added a check for NULL values in array in the C++ abstraction layer

If there is NULL, throw an error message.
Summary: New module to produce summary stats for table

Pivotal: 42751193

'summary' is a generic function used to produce summary statistics
of any data table.  The function invokes particular 'methods' from
the MADlib library to provide an overview of the data.
Improve docs for elastic-net and cross-validation
Improve cross-validation doc
Added check for GPDB<4.2 to ensure array is not treated as string
Corrected a bug caused by the previous commit
Utilities: Perform string to array for GPDB 4.1

Changes:
    - String to array was being performed for versions less than
    GPDB 4.1. This has been changed to transform for versions less
    than GPDB 4.2.
    - Summary: ntile_array was transformed from string to array
    but the case where ntile_array is NULL was not handled earlier.
Merge branch 'lda_improve' into integration

Conflicts:
	src/ports/postgres/modules/lda/lda.py_in