extdiff: wrap long lines in docstring and comments

Gettext wraps lines in the messages when it writes them to the hg.pot
file and that makes long lines look odd in the resulting .po file.

hgext/extdiff.py

@@ -146,10 +146,10 b' def dodiff(ui, repo, diffcmd, diffopts, '
         if node2:
             dir2 = snapshot(ui, repo, modadd, node2, tmproot)[0]
         elif len(common) > 1:
-            #we only actually need to get the files to copy back to the working
-            #dir in this case (because the other cases are: diffing 2 revisions
-            #or single file -- in which case the file is already directly passed
-            #to the diff tool).
+            #we only actually need to get the files to copy back to
+            #the working dir in this case (because the other cases
+            #are: diffing 2 revisions or single file -- in which case
+            #the file is already directly passed to the diff tool).
             dir2, fns_and_mtime = snapshot(ui, repo, modadd, None, tmproot)
         else:
             # This lets the diff tool open the changed file directly
@@ -169,8 +169,9 b' def dodiff(ui, repo, diffcmd, diffopts, '
                     dir1b = os.devnull
             dir2 = os.path.join(dir2root, dir2, common_file)
 
-        # Function to quote file/dir names in the argument string
-        # When not operating in 3-way mode, an empty string is returned for parent2
+        # Function to quote file/dir names in the argument string.
+        # When not operating in 3-way mode, an empty string is
+        # returned for parent2
         replace = dict(parent=dir1a, parent1=dir1a, parent2=dir1b, child=dir2)
         def quote(match):
             key = match.group()[1:]
@@ -257,13 +258,14 b' def uisetup(ui):'
             doc = _('''\
 use %(path)s to diff repository (or selected files)
 
-    Show differences between revisions for the specified files, using the
-    %(path)s program.
+    Show differences between revisions for the specified files, using
+    the %(path)s program.
 
-    When two revision arguments are given, then changes are shown between
-    those revisions. If only one revision is specified then that revision is
-    compared to the working directory, and, when no revisions are specified,
-    the working directory files are compared to its parent.\
+    When two revision arguments are given, then changes are shown
+    between those revisions. If only one revision is specified then
+    that revision is compared to the working directory, and, when no
+    revisions are specified, the working directory files are compared
+    to its parent.\
 ''') % dict(path=util.uirepr(path))
 
             # We must translate the docstring right away since it is