diff: move b85diff to mdiff module

diff: move b85diff to mdiff module

b85diff generates a binary diff, so we move this code to mdiff module
along with unidiff for text diffs. All diffing mechanisms will be in the
same place.

In an upcoming patch we will remove the responsibility to print the
index header from b85diff and move it back to patch, since it's
a patch metadata header, not part of the diff generation.

--- a/mercurial/mdiff.py	Thu Nov 15 10:55:32 2012 -0800
+++ b/mercurial/mdiff.py	Tue Nov 06 14:04:05 2012 -0800
@@ -7,7 +7,8 @@
 
 from i18n import _
 import bdiff, mpatch, util
-import re, struct
+import re, struct, base85, zlib
+from node import hex, nullid
 
 def splitnewlines(text):
     '''like str.splitlines, but only split on newlines.'''
@@ -314,6 +315,44 @@
         for x in yieldhunk(hunk):
             yield x
 
+def b85diff(to, tn):
+    '''print base85-encoded binary diff'''
+    def gitindex(text):
+        if not text:
+            return hex(nullid)
+        l = len(text)
+        s = util.sha1('blob %d\0' % l)
+        s.update(text)
+        return s.hexdigest()
+
+    def fmtline(line):
+        l = len(line)
+        if l <= 26:
+            l = chr(ord('A') + l - 1)
+        else:
+            l = chr(l - 26 + ord('a') - 1)
+        return '%c%s\n' % (l, base85.b85encode(line, True))
+
+    def chunk(text, csize=52):
+        l = len(text)
+        i = 0
+        while i < l:
+            yield text[i:i + csize]
+            i += csize
+
+    tohash = gitindex(to)
+    tnhash = gitindex(tn)
+    if tohash == tnhash:
+        return ""
+
+    # TODO: deltas
+    ret = ['index %s..%s\nGIT binary patch\nliteral %s\n' %
+           (tohash, tnhash, len(tn))]
+    for l in chunk(zlib.compress(tn)):
+        ret.append(fmtline(l))
+    ret.append('\n')
+    return ''.join(ret)
+
 def patchtext(bin):
     pos = 0
     t = []

--- a/mercurial/patch.py	Thu Nov 15 10:55:32 2012 -0800
+++ b/mercurial/patch.py	Tue Nov 06 14:04:05 2012 -0800
@@ -10,7 +10,7 @@
 import tempfile, zlib, shutil
 
 from i18n import _
-from node import hex, nullid, short
+from node import hex, short
 import base85, mdiff, scmutil, util, diffhelpers, copies, encoding, error
 import context
 
@@ -1514,44 +1514,6 @@
     finally:
         fp.close()
 
-def b85diff(to, tn):
-    '''print base85-encoded binary diff'''
-    def gitindex(text):
-        if not text:
-            return hex(nullid)
-        l = len(text)
-        s = util.sha1('blob %d\0' % l)
-        s.update(text)
-        return s.hexdigest()
-
-    def fmtline(line):
-        l = len(line)
-        if l <= 26:
-            l = chr(ord('A') + l - 1)
-        else:
-            l = chr(l - 26 + ord('a') - 1)
-        return '%c%s\n' % (l, base85.b85encode(line, True))
-
-    def chunk(text, csize=52):
-        l = len(text)
-        i = 0
-        while i < l:
-            yield text[i:i + csize]
-            i += csize
-
-    tohash = gitindex(to)
-    tnhash = gitindex(tn)
-    if tohash == tnhash:
-        return ""
-
-    # TODO: deltas
-    ret = ['index %s..%s\nGIT binary patch\nliteral %s\n' %
-           (tohash, tnhash, len(tn))]
-    for l in chunk(zlib.compress(tn)):
-        ret.append(fmtline(l))
-    ret.append('\n')
-    return ''.join(ret)
-
 class GitDiffRequired(Exception):
     pass
 
@@ -1789,7 +1751,7 @@
 
         if dodiff:
             if dodiff == 'binary':
-                text = b85diff(to, tn)
+                text = mdiff.b85diff(to, tn)
             else:
                 text = mdiff.unidiff(to, date1,
                                     # ctx2 date may be dynamic