chdman fixes for mono/unix

- call chdman as chdman and not chdman.exe
- fix parsing issue with chdman stderr output
Fix parsing of chdman stderr output.

Makes it works under mono/linux and also corrects the displayed error
message in windows.
More CHD related fixes

- CHDReturnError was not handled and would cause an exception/crash
- CHD error/filename were swapped in ErrorGrid when scanning
- Use regex when parsing chdman stdout output
Merge pull request #7 from jwestfall69/mono-chdman

chdman mono/linux fixes and improvements