cat --decode: Drop short option, use opts.get() instead of opts[]

- hg archive --no-decode has no short option, too, and maybe both could use
  -d in the future to select revisions by date.
- opts.get makes python scripts calling cat() happy, because they don't have
  to pass the new option.

mercurial/commands.py

@@ -467,7 +467,7 b' def cat(ui, repo, file1, *pats, **opts):'
                                              ctx.node()):
         fp = cmdutil.make_file(repo, opts['output'], ctx.node(), pathname=abs)
         data = ctx.filectx(abs).data()
-        if opts['decode']:
+        if opts.get('decode'):
             data = repo.wwritedata(abs, data)
         fp.write(data)
         err = 0
@@ -2768,7 +2768,7 b' table = {'
         (cat,
          [('o', 'output', '', _('print output to file with formatted name')),
           ('r', 'rev', '', _('print the given revision')),
-          ('d', 'decode', None, _('apply any matching decode filter')),
+          ('', 'decode', None, _('apply any matching decode filter')),
          ] + walkopts,
          _('hg cat [OPTION]... FILE...')),
     "^clone":

tests/test-dispatch.out

@@ -21,7 +21,7 b' options:'
 
  -o --output   print output to file with formatted name
  -r --rev      print the given revision
- -d --decode   apply any matching decode filter
+    --decode   apply any matching decode filter
  -I --include  include names matching the given patterns
  -X --exclude  exclude names matching the given patterns
 

tests/test-encode

@@ -35,8 +35,8 b' gunzip < a.gz'
 
 echo %% check hg cat operation
 hg cat a.gz
-hg cat -d a.gz | gunzip
+hg cat --decode a.gz | gunzip
 mkdir subdir
 cd subdir
 hg -R .. cat ../a.gz
-hg -R .. cat -d ../a.gz | gunzip
+hg -R .. cat --decode ../a.gz | gunzip