When we are refreshing from the index or updating the index we shouldn't
let the user cause other index based operations to occur as these would
likely conflict with the currently running operations possibly causing
some index changes to be lost.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

 * Run refresh before diff-index.
 * Load saved commit message during rescan.
 * Save current commit message (if any) during quit.
 * Add Signed-off-by line to commit buffer.
 * Batch update-index invocations through --stdin.
 * Better highlight which file is in the diff viewer.
 * Key bindings for signoff, check-in all and commit.
 * Improved formatting of status table within source.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

This is based on Paul Mackerras' gitool prototype which he offered up
to the community earlier in 2006.  Its mostly however a rewrite from
scratch of a Tcl/Tk based graphical interface for Git and the most
common commands users might need to perform.

Currently it can display the status of the current repository, and not
much else.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>