mergestate: add comments about couple of record types and minor reorder

I am trying to divide the records into certain groups and then have dedicated
objects for them. Taking baby steps in that direction.

Differential Revision: https://phab.mercurial-scm.org/D8717

mercurial/mergestate.py

@@ -41,13 +41,17 b' def _filectxorabsent(hexnode, ctx, f):'
 # Merge state record types. See ``mergestate`` docs for more.
 RECORD_LOCAL = b'L'
 RECORD_OTHER = b'O'
+# record extra information about files
+RECORD_FILE_VALUES = b'f'
+# record merge labels
+RECORD_LABELS = b'l'
+
 RECORD_MERGED = b'F'
 RECORD_CHANGEDELETE_CONFLICT = b'C'
 RECORD_MERGE_DRIVER_MERGE = b'D'
 RECORD_PATH_CONFLICT = b'P'
+
 RECORD_MERGE_DRIVER_STATE = b'm'
-RECORD_FILE_VALUES = b'f'
-RECORD_LABELS = b'l'
 RECORD_OVERRIDE = b't'
 RECORD_UNSUPPORTED_MANDATORY = b'X'
 RECORD_UNSUPPORTED_ADVISORY = b'x'