[PATCH (GITK) v2 0/4] Encoding support in GUI

Currently GUI tools don't provide enough support for viewing files that contain non-ASCII characters. This set of patches addresses this issue. The git-gui part of the series is based on patches that were in the 'pu' branch of the git-gui repository.

UPDATE: the git-gui part of the series is in master.

File encoding can be specified in the following ways:

1) It defaults to the current locale encoding.
2) It can be overridden by setting the gui.encoding option.
3) It can be further set on per-file basis by specifying
   the 'encoding' attribute in gitattributes.
4) Finally, git-gui allows directly selecting encodings
   through a popup menu.

Since git apparently cannot work with filenames in non-locale encodings anyway, I did not try to do anything about it apart from fixing some obvious bugs.

CHANGES:

- Wrote better comments for the first three patches.
- Added a patch to speed up loading of very large diffs.

GITK:
	gitk: Port new encoding logic from git-gui.
	---
	gitk |   50 +++++++++++++++++++++++++++++++++++++++++++++++---
	1 files changed, 47 insertions(+), 3 deletions(-)

	gitk: Implement file contents encoding support.
	---
	gitk |   19 ++++++++++++++++---
	1 files changed, 16 insertions(+), 3 deletions(-)

	gitk: Support filenames in the locale encoding.
	---
	gitk |   16 +++++++++++-----
	1 files changed, 11 insertions(+), 5 deletions(-)

	gitk: Implement batch lookup and caching of encoding attrs.
	---
	gitk |   35 ++++++++++++++++++++++++++++++++++-
	1 files changed, 34 insertions(+), 1 deletions(-)