Tablebase readonly mode

[Herren]

As suggested by @jodavies during the currently ongoing FORM workshop, I added an option
to the tablebase open command, allowing to open tablebases in read-only mode.
This allows to load tablebases in shared environments where not all users of the tablebases
have write permissions. In case the addto command is called on a readonly tablebase file,
an error is thrown and FORM terminates.

The syntax is simply:
TableBase "tablename.tbl" open, readonly

Some documentation on this feature is also added to the relevant manual file.

[coveralls]

coverage: 50.002% (+0.003%) from 49.999%
when pulling 7ed3e84 on Herren:tablebase_readonly
into 83e3d41 on vermaseren:master.

[jodavies]

Currently, if you attempt to open a non-existing tablebase in readonly mode, there is no error and the file is created. I think this case should print an error and terminate FORM.

[Herren]

Please have a look at the change. It should work now.

[jodavies]

Thanks, this works. Could you finally add test cases in check/features.frm for the failure modes, trying to add to an opened readonly table, and trying to open a non-existing table in readonly mode?

You can run multiple form scripts in a single test case like this: jodavies@9a5e42d

[Herren]

I attempted to add two tests, but I think I don't entirely understand how the test framework works....

[jodavies]

On my system, the parform valgrind error is also an error in form, but not so on the runner?

Anyway, in GetDbase in minos.c I think you can just Terminate(-1); after your error message.

[Herren]

Done.

[coveralls]

coverage: 48.661% (+0.7%) from 47.92%
when pulling 79e2b15 on Herren:tablebase_readonly
into f2df9bf on vermaseren:master.

[jodavies]

Ah, it seems #573 has broken the 32bit tests.

[tueda]

On the master branch, even in 32-bit containers, FORM_IGNORE_DEPRECATION is set and CI runs fine.

Maybe rebasing will fix the CI failures?

[jodavies]

I think this looks good now. Any further comments, @tueda ?