implementing execute_array/execute_for_fetch useful test code (and GCI)

In a rare moment (I hope) of stupidity last weekend when I was a little 
bored (bad cold stopped me doing what I really wanted to do) I looked 
through the DBD::ODBC TO_DO list and saw the "implement 
execute_array/execute_for_fetch" item which has been in that file for 
years. I know for sure implementing it will be a lot faster than using 
DBI's default methods (which effectively do a row at a time) mostly 
because I wrote an ODBC tutorial years ago showing how much faster 
binding arrays of parameters is 
(http://www.easysoft.com/products/data_access/odbc_odbc_bridge/performance_white_paper.html)  
but I also knew it would be a PITA to write. The main problem is that 
DBD::ODBC has loads of workarounds for broken drivers and special cases.

Anyway, having started it I resolved to finish it and I had a working 
version (as far as I knew and not withstanding special workarounds). My 
final test was to run it through a test I wrote for 
execute_array/execute_for_fetch for DBD::ODBC in t/70execute_array.t and 
added to DBD::Oracle a while later (when I found DBD::Oracle failed 
quite a number of the tests). It failed quite a number of tests and all 
the failures were legitimate ones like not returning undef if any row 
failed and not calling set_err if any row failed. If anyone else ever 
contemplates adding execute_array/execute_for_fetch support to a DBD I 
strongly recommend you get a copy of t/70execute_array from DBD::ODBC or 
DBD::Oracle (the latter could be a little out of date sometimes) and use 
it as a test case. It does not use any complicated SQL and so should be 
easy to adapt for other DBDs.

This test code probably find its way into DBI at some stage but it would 
need checking for SQL syntax in particular. Currently it just uses:

create table a_table (a integer primary key, b char(20))
drop table a_table
delete from a_table
insert into a_table values(?,?)
select * from a_table
update a_table set a_column = ? where a_column = ?

Obviously, it isn't going to work for read-only DBDs like DBD::Sponge 
and DBD::Sys.

Perhaps we should have added some DBI tasks to GCI (#gci) 
(http://www.google-melange.com/gci/org/google/gci2011/tpf,  
http://wiki.enlightenedperl.org/gci2011) especially for testing.

Martin