[jgit-dev] Config should throw IOException instead of IllegalArgumentExc

[Marc Strapetz <marc.strapetz@xxxxxxxxxxx>]

Those methods of *Config which are doing validation currently throw an
IllegalArgumentException in case of invalid values. E.g. DiffConfig will
do that for:

diff.rename=3000

or

diff.renamelimit=foobar

As config files can be edited by a user, an IOException or some custom
derivate would be more appropriate. Should I fix that and submit a patch?

-Marc