restG4 not working if user doesn't have permissions in cwd

[lobis]

We should be able to do do:

restG4 -o some-directory-with-write-permissions some.rml

but it currently fails if restG4 is launched from a directory without write permissions, even though you should only need to read the required files and not write.

Looks like the problem is related to TRestRun

-- Warning : no input file added
-- Error : TRestRun: Output path does not exist or it is not writable.
-- Error : Path : ./

It is performing some kind of check on write permissions for the directory after being loaded from an rml from the same directory. We should not return an error when this happens, perhaps a warning.