test command parsing and dispatch

  $ "$TESTDIR/hghave" no-outer-repo || exit 80

  $ dir=`pwd`

  $ hg init a

  $ cd a

  $ echo a > a

  $ hg ci -Ama

  adding a

Missing arg:

  $ hg cat

  hg cat: invalid arguments

  hg cat [OPTION]... FILE...

  output the current or given revision of files

  options:

   -o --output FORMAT        print output to file with formatted name

   -r --rev REV              print the given revision

      --decode               apply any matching decode filter

   -I --include PATTERN [+]  include names matching the given patterns

   -X --exclude PATTERN [+]  exclude names matching the given patterns

  [+] marked option can be specified multiple times

  use "hg help cat" to show the full help text

  [255]

[defaults]

  $ hg cat a

  a

  $ cat >> $HGRCPATH <<EOF

  > [defaults]

  > cat = -r null

  > EOF

  $ hg cat a

  a: no such file in rev 000000000000

  [1]

No repo:

  $ cd $dir

  $ hg cat

  [255]