Added dbgflags.py for easier flag debugging

dbgerr.py and dbgtag.py have proven to be incredibly useful for quick
debugging/introspection, so I figured why not have more of that.

My favorite part is being able to quickly see all flags set on an open
file handle:

  (gdb) p file.o.o.flags
  $2 = 24117517
  (gdb) !./scripts/dbgflags.py o 24117517
  LFS_O_WRONLY   0x00000001  Open a file as write only
  LFS_O_CREAT    0x00000004  Create a file if it does not exist
  LFS_O_EXCL     0x00000008  Fail if a file already exists
  LFS_O_DESYNC   0x00000100  Do not sync or recieve file updates
  LFS_o_REG      0x01000000  Type = regular-file
  LFS_o_UNFLUSH  0x00100000  File's data does not match disk
  LFS_o_UNSYNC   0x00200000  File's metadata does not match disk
  LFS_o_UNCREAT  0x00400000  File does not exist yet

The only concern is if dbgflags.py falls out-of-sync often, I suspect
flag encoding will have quite a bit more churn than flags/tags. But we
can always drop this script in the future if this turns into a problem.

---

While poking around this also ended up with a bunch of other small
changes:

- Added LFS_*_MODE masks for consistency with other "type<->flag
  embeddings"

- Added compat flag comments

- Adopted lowercase prefix for internal flags (LFS_o_ZOMBIE), though
  not sure if I'll keep this yet...

- Tweaked dbgerr.py to also match ERR_ prefixes and to ignore case

scripts/dbgerr.py

@@ -31,35 +31,30 @@ def main(errs, *,
     import builtins
     list_, list = list, builtins.list
 
+    lines = []
     # list all known error codes
     if list_:
-        # first find the widths
-        w = [0, 0]
         for n, e, h in ERRS:
-            w[0] = max(w[0], len('LFS_ERR_')+len(n))
-            w[1] = max(w[1], len(str(e)))
-
-        # print
-        for n, e, h in ERRS:
-            print('%-*s  %-*s  %s' % (
-                    w[0], 'LFS_ERR_'+n,
-                    w[1], e,
-                    h))
+            lines.append(('LFS_ERR_'+n, str(e), h))
 
     # find these errors
     else:
         def find_err(err):
             # find by LFS_ERR_+name
             for n, e, h in ERRS:
-                if 'LFS_ERR_'+n == err:
+                if 'LFS_ERR_'+n == err.upper():
+                    return n, e, h
+            # find by ERR_+name
+            for n, e, h in ERRS:
+                if 'ERR_'+n == err.upper():
                     return n, e, h
             # find by name
             for n, e, h in ERRS:
-                if n == err:
+                if n == err.upper():
                     return n, e, h
             # find by E+name
             for n, e, h in ERRS:
-                if 'E'+n == err:
+                if 'E'+n == err.upper():
                     return n, e, h
             try:
                 # find by err code
@@ -78,9 +73,22 @@ def main(errs, *,
         for err in errs:
             try:
                 n, e, h = find_err(err)
-                print('%s %s %s' % ('LFS_ERR_'+n, e, h))
+                lines.append(('LFS_ERR_'+n, str(e), h))
             except KeyError:
-                print('%s ?' % err)
+                lines.append(('?', err, 'Unknown err code'))
+
+    # first find widths
+    w = [0, 0]
+    for l in lines:
+        w[0] = max(w[0], len(l[0]))
+        w[1] = max(w[1], len(l[1]))
+
+    # then print results
+    for l in lines:
+        print('%-*s  %-*s  %s' % (
+                w[0], l[0],
+                w[1], l[1],
+                l[2]))
 
 
 if __name__ == "__main__":