Fix problems with missing ulong

On OS X, there were some problems with ulong type (see issue #9).
Because CRC32 should always be 32 bits long, it was exchanged to
uint32_t, which should be more widespread type. Still there exists
uLong, which is zlib-specific.

src/xsdc.c

@@ -124,7 +124,7 @@ DecrError decryptData(void *buffer, uint32_t *bufferSize, void *outputBuffer, vo
     return DD_OK;
 }
 
-ulong countCrc(FILE *f, uint32_t hdrSize)
+uint32_t countCrc(FILE *f, uint32_t hdrSize)
 {
     void *buffer = malloc(0x1000);
     uLong crc = crc32(0L, Z_NULL, 0);
@@ -135,7 +135,7 @@ ulong countCrc(FILE *f, uint32_t hdrSize)
         crc = crc32(crc, (Bytef*)buffer, bytes);
     }
     free(buffer);
-    return crc;
+    return (uint32_t) crc;
 }
 
 DecrError loadHeader(FILE *f, Header *hdr, uint32_t hdrSize, UnpackData *ud)

src/xsdc.h

@@ -143,7 +143,7 @@ uint32_t getDataOutputSize(uint32_t inputSize);
 /*
  * count and return crc of sdc file's data area
  */
-ulong countCrc(FILE *f, uint32_t hdrSize);
+uint32_t countCrc(FILE *f, uint32_t hdrSize);
 
 /*
  * load sdc file header from current position in F into HDR buffer