Allow symlink blobs in trees during fast-import.

If a frontend is smart enough to import a symlink then we should
let them do so.  We'll assume that they were smart enough to first
generate a blob to hold the link target, as that's how symlinks
get represented in GIT.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

fast-import.c

@@ -1017,6 +1017,7 @@ static void file_change_m(struct branch *b)
 	switch (mode) {
 	case S_IFREG | 0644:
 	case S_IFREG | 0755:
+	case S_IFLNK:
 	case 0644:
 	case 0755:
 		/* ok */