scripts: Dropped list/tuple distinction in Rbyd.fetch

Also tweaked how we fetch shrubs, adding Rbyd.fetchshrub and
Btree.fetchshrub instead of overloading the bd argument.

Oh, and also added --trunk to dbgmtree.py and dbglfs.py. Actually
_using_ --trunk isn't advised, since it will probably just result in a
corrupted filesystem, but these scripts are for accessing things that
aren't normally allowed anyways.

The reason for dropping the list/tuple distinction is because it was a
big ugly hack, unpythonic, and likely to catch users (and myself) by
surprise. Now, Rbyd.fetch and friends always require separate
block/trunk arguments, and the exercise of deciding which trunk to use
is left up to the caller.

scripts/dbgbmap.py

@@ -97,10 +97,10 @@ def bdgeom(s):
         return int(s, b)
 
 # parse some rbyd addr encodings
-# 0xa       -> [0xa]
-# 0xa.c     -> [(0xa, 0xc)]
-# 0x{a,b}   -> [0xa, 0xb]
-# 0x{a,b}.c -> [(0xa, 0xc), (0xb, 0xc)]
+# 0xa       -> (0xa,)
+# 0xa.c     -> ((0xa, 0xc),)
+# 0x{a,b}   -> (0xa, 0xb)
+# 0x{a,b}.c -> ((0xa, 0xc), (0xb, 0xc))
 def rbydaddr(s):
     s = s.strip()
     b = 10
@@ -131,7 +131,7 @@ def rbydaddr(s):
         else:
             addr.append(int(s, b))
 
-    return addr
+    return tuple(addr)
 
 def crc32c(data, crc=0):
     crc ^= 0xffffffff