nodes: expand/comment the magic nodes so they are more easily searchable

We just encountered `000000000000modified`, and it was quite annoying to search
for these, even though I knew they existed.  For those that don't know that they
exist, this is essentially impossible to search for :)

(Technically we encountered it in its hex form,
3030303030303030303030306d6f646966696564, so I'm adding comments with those
forms in case that's helpful to people in the future).

Differential Revision: https://phab.mercurial-scm.org/D4331

mercurial/node.py

@@ -21,20 +21,25 b' def bin(s):'
         raise TypeError(e)
 
 nullrev = -1
+# In hex, this is '0000000000000000000000000000000000000000'
 nullid = b"\0" * 20
 nullhex = hex(nullid)
 
 # Phony node value to stand-in for new files in some uses of
 # manifests.
-newnodeid = '!' * 20
-addednodeid = ('0' * 15) + 'added'
-modifiednodeid = ('0' * 12) + 'modified'
+# In hex, this is '2121212121212121212121212121212121212121'
+newnodeid = '!!!!!!!!!!!!!!!!!!!!'
+# In hex, this is '0000000000000000000000000000006164646564'
+addednodeid = '000000000000000added'
+# In hex, this is '0000000000000000000000006d6f646966696564'
+modifiednodeid = '000000000000modified'
 
 wdirfilenodeids = {newnodeid, addednodeid, modifiednodeid}
 
 # pseudo identifiers for working directory
 # (they are experimental, so don't add too many dependencies on them)
 wdirrev = 0x7fffffff
+# In hex, this is 'ffffffffffffffffffffffffffffffffffffffff'
 wdirid = b"\xff" * 20
 wdirhex = hex(wdirid)