[PATCH 0/9 v6] difftool: teach command to perform directory diffs

Changes in v6:
  - Rebased series to insure Getopt::Long worked correctly from the start.
  - Squashed commits that added tests into the commits that added the
    new features.

Series Overview:

'git difftool' is a very useful command that allows git diffs to be opened in an external tool. Currently, difftool opens a separate instance of the external tool for each file that changed. This can be tedious when many files have changed.

This series teaches difftool to perform directory diffs, so that all file changes can be opened/reviewed in a single instance of the external tool.

This is the second phase of development for this feature. The first phase was added as a separate command (git diffall) in 1252bbe (contrib: add git-diffall script). During review of that script on the Git developers list, an informal development roadmap was suggested [1]. The next phase of that plan is to integrate the 'git-diffall' feature into 'difftool'. This series gets that done.

[1]: http://thread.gmane.org/gmane.comp.version-control.git/191297/focus=191383

Tim Henigan (9):
  difftool: parse options using Getopt::Long
  difftool: add '--no-gui' option
  difftool: exit(0) when usage is printed
  difftool: remove explicit change of PATH
  difftool: stop appending '.exe' to git
  difftool: eliminate setup_environment function
  difftool: replace system call with Git::command_noisy
  difftool: teach difftool to handle directory diffs
  difftool: print list of valid tools with '--tool-help'

 Documentation/git-difftool.txt |   17 ++-
 git-difftool--helper.sh        |   19 ++-
 git-difftool.perl              |  264 +++++++++++++++++++++++++++-------------
 t/t7800-difftool.sh            |   57 +++++++++
 4 files changed, 262 insertions(+), 95 deletions(-)