Bug 36020

As discussed on tomcat-dev I contribute a patch for MemoryUserDatabase that:

1) Logs a warning, if the persistance directory is not writeable (instead of an
ugly Exception)
2) Implements an additional attribute "readonly" (default: false) that one can
use to not get the warning in cases, where it's clear, that the directory is not
writeable.

The patch does not include a changelog-Patch, because that changes too often.
CVS Head and 5.5.10 is the same for all files with changes.

The Warn message is only contained in the english LocalString.properties. Anyone
who could do es/fr/ja ?

I think, at the moment there is no documentation for Userdatabase, so no place
to add "readonly" information. If I'm wrong, please correct me.

I'll try to add the readonly info to admin too (later).

Last question: the close() for the MemoryUserDatabase is never called,
especially not during shutdown of tomcat. Anyone with a good hint, where to look
for adding a hook to close MemoryUserDatabase during tomcat shutdown?