getting rid of some compilation warnings

[Sebastian Reitenbach]

Hi,

I try to cleanup sope/ogo gsmake2 branch, also to get rid of compilation 
warnings.

one of them is:

NGImap4ResponseNormalizer.m:686: warning: multiple declarations for 
method `hasPrefix:'
/usr/local/include/Foundation/NSString.h:340: warning: using 
`-(BOOL)hasPrefix:(NSString *)aString'
../../sope-core/NGExtensions/NGExtensions/NSData+misc.h:29: warning: 
also found `-(BOOL)hasPrefix:(NSData *)_data'

The header file NSData+misc.h looks like this:
#import <Foundation/NSData.h>

@interface NSData(misc)

- (BOOL)hasPrefix:(NSData *)_data;
- (BOOL)hasPrefixBytes:(const void *)_bytes length:(unsigned)_len;

@end

the code where the warning is emitted looks like this:

static inline NSArray *
_imapFlags2Flags(NGImap4ResponseNormalizer *self, NSArray *_flags)  
{

id obj;
...
 while ((obj = [enumerator nextObject])) {
   if ([obj isNotEmpty]) {
     if ([obj hasPrefix:@"\\"])
       objs[cnt] = [obj substringFromIndex:1];
     else
       objs[cnt] = obj;
     cnt++;
   }
 }
...
}

my guess is that obj is id, and the compiler doesn't know, which one to use.
Is there a way to get rid of the warning?

cheers,
Sebastian