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
  abort: no repository found in '$TESTTMP' (.hg not found)!
  [255]