* CharConverterTest.cs: Added tests for ConvertFrom and ConvertTo.

* CharConverterTest.cs: Added tests for ConvertFrom and ConvertTo.
* CultureInfoConverterTest.cs: Added tests for ConvertFrom and
ConvertTo.
* CharConverter.cs (ConvertFrom): Avoid NRE when value is null.
Provide more info when left of value > 1.
* CultureInfoConverter.cs (ConvertFrom): Avoid NRE when value is null.
On 2.0 profile, use case-sensitive comparison for (Default) value.
Use case-insensitive comparing when value is considered as displayname.
Provide more info in exception message.
(ConvertTo): Use '(Default)' instead of '(default)' for invariant
culture.
* System_test.dll.sources: Added CharConverterTest.cs and
CultureInfoConverterTest.cs.

svn path=/trunk/mcs/; revision=95995