RealtionalDatabase DataConnectory documentation

[Rod Widdowson]

I (think) that I've finished this.

The tree starting at:
https://wiki.shibboleth.net/confluence/display/IDP30/RelationalDatabaseConne
ctor

I have pretty much written it from the source and, where needed, the
documentation of the external libraries we configure.

I'd appreciate it if you could review it for the usual typos, but mostly for
accuracy (this aimed particularly Daniel and Scott since I might have missed
a nuance somewhere).

In writing this a couple of things occurred to me:

1) I haven’t a clue how JNDI works and so the documentation I wrote is less
than helpful (especially the example)
(https://wiki.shibboleth.net/confluence/display/IDP30/ContainerManagedConnec
tion)

2) Is it worth shimming the C3PO pool element we use for
ApplicationManagedConnection to allow XML durations to be specified?  I
think not since the legacy configuration is a mishmash of seconds and
milliseconds and adding durations would probably confuse rather than help.

3) (An observation rather than a question) There are three different
mechanisms to inject Spring Beans:  The freestanding config resource, and
beans specified as attributes (velocityEngine and mappingStrategyRef) and as
element contents (<BeanManagedConnection> and <ResultCacheBean>).  We are
stuck with that for now and I can see why we need all three it was just
slightly difficult to write up.

Thanks

Rod