Update to new APIs for reading/writing plists

These do not cause a problem yet, but the new APIs follow proper Cocoa memory management rules and will make upgrading to ARC easier.

Also, since we now return an NSError instead of an NSString, we should not expect upon successful completion that these methods will return nil for the passed NSError object.
Use (Core) Foundation data types
camelCase local variables
Prefer BOOL instead of bool

There is no need to mix C++ for this case.
Use Objective-C literals and boxing
Use anonymous categories to declare private methods and properties

Anonymous and named categories actual behave differently. Using the latter, prevents us from declaring (private) properties.
NSAutoReleasePool → @autoreleasepool
Update to ARC
Don't use the pre-processor to declare a string constant

Also, renamed DialogServerConnectionName → kDialogServerConnectionName. This is more consistent with the TextMate coding style.
Use proper exit codes
Remove debug statements
Remove include guard