git-gui: Do not reset author details on amend

git commit --amend preserves the author details unless --reset-author is
given.

git-gui discards the author details on amend.

Fix by reading the author details along with the commit message, and
setting the appropriate environment variables required for preserving
them.

Reported long ago in the mailing list[1].

[1] http://article.gmane.org/gmane.comp.version-control.git/243921

Signed-off-by: Orgad Shaneh <orgad.shaneh@audiocodes.com>

git-gui/lib/commit.tcl

@@ -1,8 +1,13 @@
 # git-gui misc. commit reading/writing support
 # Copyright (C) 2006, 2007 Shawn Pearce
 
+set author_name ""
+set author_email ""
+set author_date ""
+
 proc load_last_commit {} {
 	global HEAD PARENT MERGE_HEAD commit_type ui_comm
+	global author_name author_email author_date
 	global repo_config
 
 	if {[llength $PARENT] == 0} {
@@ -34,6 +39,10 @@ You are currently in the middle of a merge that has not been fully completed.  Y
 					lappend parents [string range $line 7 end]
 				} elseif {[string match {encoding *} $line]} {
 					set enc [string tolower [string range $line 9 end]]
+				} elseif {[regexp "author (.*)\\s<(.*)>\\s(\\d.*$)" $line all name email time]} {
+					set author_name $name
+					set author_email $email
+					set author_date $time
 				}
 			}
 			set msg [read $fd]
@@ -107,8 +116,12 @@ proc do_signoff {} {
 
 proc create_new_commit {} {
 	global commit_type ui_comm
+	global author_name author_email author_date
 
 	set commit_type normal
+	set author_name ""
+	set author_email ""
+	set author_date ""
 	$ui_comm delete 0.0 end
 	$ui_comm edit reset
 	$ui_comm edit modified false
@@ -327,6 +340,7 @@ proc commit_committree {fd_wt curHEAD msg_p} {
 	global ui_comm selected_commit_type
 	global file_states selected_paths rescan_active
 	global repo_config
+	global env author_name author_email author_date
 
 	gets $fd_wt tree_id
 	if {[catch {close $fd_wt} err]} {
@@ -366,6 +380,11 @@ A rescan will be automatically started now.
 		}
 	}
 
+	if {$author_name ne ""} {
+		set env(GIT_AUTHOR_NAME) $author_name
+		set env(GIT_AUTHOR_EMAIL) $author_email
+		set env(GIT_AUTHOR_DATE) $author_date
+	}
 	# -- Create the commit.
 	#
 	set cmd [list commit-tree $tree_id]