Support for generating a Greenplum gppkg

Jira: MADLIB-577

The targets are called gppkg_<version> where <version> is of form "4_2". It depends on ${CPACK_PACKAGE_FILE_NAME}.rpm and use the same files (from the _CPack_Packages directory), but it will exclude all files that are specific to different ports.

The initial gppkg version number for MADlib v0.4 will be 1.1 (note that v0.3 was 1.0).
Build system: Meta target to generate all supported Greenplum gppkg at once

Jira: MADLIB-577
In preparation for design document: Added UseLATEX.cmake to repository

Jira: MADLIB-522

Changes:
- Imported UseLATEX.cmake 1.9.4 from <http://www.cmake.org/Wiki/images/8/80/UseLATEX.cmake>.
Author: Kenneth Moreland <kmorel@sandia.gov>
Copyright 2004 Sandia Corporation.
Under the terms of Contract DE-AC04-94AL85000, there is a non-exclusive license for use of this work by or on behalf of the U.S. Government. Redistribution and use in source and binary forms, with or without modification, are permitted provided that this Notice and any statement of authorship are reproduced on all copies.
- Added several LaTeX files suffixes to .gitignore
Documentation: Initial version MADlib design document (using k-means as example)

Jira: MADLIB-522

Build system:
- Added UseLATEX.cmake, version 1.9.0, by Kenneth Moreland
- Slight modifications to UseLATEX.cmake
Design document: Introduction to SVD module

Jira: MADLIB-572

replaced package minted by listings in doc/design

updated lstset for listings package
Design Document: Separated chapters into different files

Jira: MADLIB-522

The cmake target name for compiling the design document is 'design_pdf'.
Added flex and bison to the list of dependencies in ReadMe_Build.txt

Jira: None

As reported and discussed on the MADlib mailing list: <http://thread.gmane.org/gmane.comp.statistics.madlib.user/218>
Added a sampling module, currently containing only weighted_sample().

Jira: MADLIB-584

Sampling module:
- Added a data-parallel UDA for weighted sampling of a single row
C++ AL:
- Added a boost/TR1-style front-end to PostgreSQL's random number generator.
UseLATEX.cmake: Never add dvi target to default target

Jira: None

The standard UseLATEX.cmake always adds at least one LaTeX target to the default target. However, not every time we run make, we actually want to update our LaTeX documents. I changed UseLATEX.cmake so that it only adds a LaTeX target to the default target if DEFAULT_PDF or DEFAULT_SAFEPDF are set.
Hypothesis tests now also installed on PG8.4/GP4.0

Jira: MADLIB-584

This provides a fix for the install-check errors on PG8.4/GP4.0.
Background:
It is convenient to have the hypothesis tests available for the random-
sampling unit tests. Therefore, they are now also installed on versions
of PostgreSQL/Greenplum that do not support ordered aggregates. Of 
course, some hypothesis tests rely on ordered aggregates, and these
tests will still not work correctly but raise an error instead. I
therefore disabled unit tests for those hypothesis tests on PG8.4/GP4.0
(currently ks_test, mw_test, and wsr_test).
Improved Design Doc: Low-rank Matrix Factorization

JIRA: MADLIB-578
1. added more descriptions after the pseudo-code
2. made the symbols consistent with the code
3. added some more citations

(minor additional changes by Florian Schoppmann as discussed in
pull request #179)