WL#3720: Enhanced Numeric Functions

Fully support SQL:2003 non-core standard feature
T621 "Enhanced numeric functions".

These T621 functions are already in MySQL:
CEILING, COVAR_POP, COVAR_POP, EXP LN, SQRT,
STDDEV_POP, STDDEV_SAMP, VAR_POP, VAR_SAMP.

These T621 functions are not in MySQL, are in
Oracle, and are in PostgreSQL 8.2:
CORR ("correlation coefficient"), REGR_SLOPE
REGR_INTERCEPT REGR_COUNT REGR_R2 REGR_AVGX
REGR_SXX REGR_SYY (all REGR functions are
linear regression functions). The ANSI/ISO
term is "binary set functions", the PostgreSQL
term is "statistical functions".

This T621 function is not in MySQL, is in Oracle,
and is not in PostgreSQL 8.2: WIDTH_BUCKET.
It's not part of this task because it's already
part of another task: WL#2266 OLAP.


References
----------

Oracle, "REGR_ (Linear Regression) Functions"
http://download-west.oracle.com/docs/cd/B19306_01/server.102/b14200/functions132.htm#i85922

"SQL In a Nutshell", "Chapter 4: SQL Functions", Kevin Kline
http://www.oreilly.com/catalog/sqlnut2/chapter/ch04.pdf
In the "ANSI SQL Aggregate Functions" sample chapter,
there is a description of most of these functions and the
DBMSs that support them, as of 2004.

"ora_funcs: A set of UDFs that implement some Oracle specific SQL functions not
available in MySQL"
http://forge.mysql.com/projects/view.php?id=100