Made significant progress around inlined-file state during mdir commits

The main improvement is moving the special inlined-file compaction logic
up into lfsr_mdir_compact__. We only need this logic for files stored in
mdirs, and thanks to its recursive nature, we weren't getting any
benefit from handling this at a lower level anyways.

This is a nice logical restructuring that probably saves a bit of code
cost in the end.

Another significant improvement is moving the staging copy of the
inlined tree's state up into the file struct itself. This solves the
problem of needed N copies of temporary inlined state when you have N
open files.

It also provides a central place to stage changes when compacting
inlined trees, which happens across several different places in the mdir
commit logic. Though some may see this as more a hack than a feature.

Also note-worthy, but minor: these changes required an additional
opened-mdir linked-list to know when the mdir is a file and may contain
an inlined tree.

scripts/dbglfs.py

@@ -874,6 +874,7 @@ def frepr(mdir, rid, tag):
             did, _ = fromleb128(data)
             did = '0x%x' % did
         return 'bookmark %s' % did
+
     elif tag == TAG_DIR:
         # read the did
         did = '?'
@@ -882,6 +883,25 @@ def frepr(mdir, rid, tag):
             did, _ = fromleb128(data)
             did = '0x%x' % did
         return 'dir %s' % did
+
+    elif tag == TAG_REG:
+        size = 0
+        structs = []
+        # inlined?
+        done, rid_, tag_, w_, j, d, data, _ = mdir.lookup(rid, TAG_INLINED)
+        if not done and rid_ == rid and tag_ == TAG_INLINED:
+            size = max(size, len(data))
+            structs.append('inlined 0x%x.%x %d' % (mdir.block, j+d, len(data)))
+        # inlined tree?
+        done, rid_, tag_, w_, j, d, data, _ = mdir.lookup(rid, TAG_TRUNK)
+        if not done and rid_ == rid and tag_ == TAG_TRUNK:
+            d = 0
+            trunk, d_ = fromleb128(data[d:]); d += d_
+            weight, d_ = fromleb128(data[d:]); d += d_
+            size = max(size, weight)
+            structs.append('trunk 0x%x.%x' % (mdir.block, trunk))
+        return 'reg %s' % ', '.join(it.chain(['%d' % size], structs))
+
     else:
         return 'type 0x%02x' % (tag & 0xff)