[PATCH (GITK,GIT-GUI,DOCS) 0/7] Improve gui blame and gitk integration

This series improves git gui blame usability by providing better integration with gitk, and thus supporting more ways of navigating the history.

Viewing the history context is especially useful if the repository is imported from a VCS without atomic commits, and thus related changes are often fragmented into a sequence of several commit objects.

Note: Show History Context won't work if gitk is unpatched.

Usage scenario:

	1. Start git gui blame from an IDE macro; use
	   --line=... to immediately scroll to the same
	   position as the IDE editor.

	2. Use 'Show History Context' to view the diff
	   and surrounding commits.
	   
	3. Use 'Blame parent commit' in gitk to explore
	   blame for other files touched by the same commit.
	
	4. If the change is irrelevant (e.g. some variable
	   was renamed), close gitk and use 'Blame Parent Commit'
	   in Gui Blame to restart search.

GITK:
	gitk: Allow overriding the default commit.
	---
	 gitk |   21 ++++++++++++++++++++-
	 1 files changed, 20 insertions(+), 1 deletions(-)
 
	gitk: Support calling git gui blame from gitk.
	---
	 gitk |   23 +++++++++++++++++++++++
	 1 files changed, 23 insertions(+), 0 deletions(-)
 
GIT-GUI: 
	git-gui: Support starting gitk from Gui Blame
	---
	 git-gui.sh     |    1 +
	 lib/blame.tcl  |   55 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
	 lib/option.tcl |    1 +
	 3 files changed, 55 insertions(+), 2 deletions(-)
	 
	git-gui: Support passing blame to a parent commit.
	---
	 lib/blame.tcl |   48 ++++++++++++++++++++++++++++++++++++++----------
	 1 files changed, 38 insertions(+), 10 deletions(-)

	git-gui: Better positioning in Blame Parent Commit
	---
	 lib/blame.tcl |   65 +++++++++++++++++++++++++++++++++++++++++++++++++++++---
	 1 files changed, 61 insertions(+), 4 deletions(-)

	git-gui: Allow specifying an initial line for git gui blame.
	---
	 git-gui.sh      |   13 +++++++++++--
	 lib/blame.tcl   |    4 ++--
	 lib/browser.tcl |    2 +-
	 3 files changed, 14 insertions(+), 5 deletions(-)

DOCS:
	Document new options of gui tools.
	---
	 Documentation/config.txt  |   14 ++++++++++++++
	 Documentation/git-gui.txt |    5 +++++
	 Documentation/gitk.txt    |    5 +++++
	 3 files changed, 24 insertions(+), 0 deletions(-)