Enable --compare-dest to work in combination with --always-checksum.

Problem and suggested patch from Dean Scothern dino@cricinfo.com (although
I re-wrote the patch).

generator.c

@@ -35,6 +35,7 @@ extern int size_only;
 extern int io_timeout;
 extern int remote_version;
 extern int always_checksum;
+extern char *compare_dest;
 
 
 /* choose whether to skip a particular file */
@@ -49,6 +50,15 @@ static int skip_file(char *fname,
 	   of the file time to determine whether to sync */
 	if (always_checksum && S_ISREG(st->st_mode)) {
 		char sum[MD4_SUM_LENGTH];
+		char fnamecmpdest[MAXPATHLEN];
+
+		if (compare_dest != NULL) {
+			if (access(fname, 0) != 0) {
+				slprintf(fnamecmpdest,MAXPATHLEN,"%s/%s",
+						    compare_dest,fname);
+				fname = fnamecmpdest;
+			}
+		}
 		file_checksum(fname,sum,st->st_size);
 		if (remote_version < 21) {
 			return (memcmp(sum,file->sum,2) == 0);