git-gui: Cleaned up error message formatting.

Added an extra blank line between the first line of each error message
and the rest of the message, as usually the rest of the message is
coming from Tcl or is the stderr output of a git command we tried to
invoke.  This makes it easier to read the output (if any).
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

git-gui

@@ -73,7 +73,8 @@ proc error_popup {msg} {
 			end]
 		append title {)}
 	}
-	tk_messageBox -parent . \
+	tk_messageBox \
+		-parent . \
 		-icon error \
 		-type ok \
 		-title "$title: error" \
@@ -84,8 +85,10 @@ proc error_popup {msg} {
 ##
 ## repository setup
 
-if {[catch {set cdup [exec git rev-parse --show-cdup]} err]} {
-	error_popup "Cannot find the git directory:\n$err"
+if {   [catch {set cdup [exec git rev-parse --show-cdup]} err]
+	|| [catch {set gitdir [exec git rev-parse --git-dir]} err]} {
+	catch {wm withdraw .}
+	error_popup "Cannot find the git directory:\n\n$err"
 	exit 1
 }
 if {$cdup != ""} {
@@ -93,11 +96,6 @@ if {$cdup != ""} {
 }
 unset cdup
 
-if {[catch {set gitdir [exec git rev-parse --git-dir]} err]} {
-	error_popup "Cannot find the git directory:\n$err"
-	exit 1
-}
-
 if {$appname == {git-citool}} {
 	set single_commit 1
 }
@@ -420,7 +418,7 @@ proc show_diff {path {w {}} {lno {}}} {
 			set diff_active 0
 			unlock_index
 			set ui_status_value "Unable to display [escape_path $path]"
-			error_popup "Error loading file:\n$err"
+			error_popup "Error loading file:\n\n$err"
 			return
 		}
 		$ui_diff conf -state normal
@@ -437,7 +435,7 @@ proc show_diff {path {w {}} {lno {}}} {
 		set diff_active 0
 		unlock_index
 		set ui_status_value "Unable to display [escape_path $path]"
-		error_popup "Error loading diff:\n$err"
+		error_popup "Error loading diff:\n\n$err"
 		return
 	}
 
@@ -523,7 +521,7 @@ proc load_last_commit {} {
 			set msg [string trim [read $fd]]
 			close $fd
 		} err]} {
-		error_popup "Error loading commit data for amend:\n$err"
+		error_popup "Error loading commit data for amend:\n\n$err"
 		return
 	}
 
@@ -655,10 +653,8 @@ proc commit_stage2 {fd_wt curHEAD msg} {
 	global file_states
 
 	gets $fd_wt tree_id
-	close $fd_wt
-
-	if {$tree_id == {}} {
-		error_popup "write-tree failed"
+	if {$tree_id == {} || [catch {close $fd_wt} err]} {
+		error_popup "write-tree failed:\n\n$err"
 		set commit_active 0
 		set ui_status_value {Commit failed.}
 		unlock_index
@@ -679,7 +675,7 @@ proc commit_stage2 {fd_wt curHEAD msg} {
 				}
 				close $fd_mh
 			} err]} {
-			error_popup "Loading MERGE_HEAD failed:\n$err"
+			error_popup "Loading MERGE_HEAD failed:\n\n$err"
 			set commit_active 0
 			set ui_status_value {Commit failed.}
 			unlock_index
@@ -692,7 +688,7 @@ proc commit_stage2 {fd_wt curHEAD msg} {
 	}
 	lappend cmd << $msg
 	if {[catch {set cmt_id [eval exec $cmd]} err]} {
-		error_popup "commit-tree failed:\n$err"
+		error_popup "commit-tree failed:\n\n$err"
 		set commit_active 0
 		set ui_status_value {Commit failed.}
 		unlock_index
@@ -713,7 +709,7 @@ proc commit_stage2 {fd_wt curHEAD msg} {
 	}
 	set cmd [list git update-ref -m $reflogm HEAD $cmt_id $curHEAD]
 	if {[catch {eval exec $cmd} err]} {
-		error_popup "update-ref failed:\n$err"
+		error_popup "update-ref failed:\n\n$err"
 		set commit_active 0
 		set ui_status_value {Commit failed.}
 		unlock_index
@@ -1481,12 +1477,12 @@ proc do_signoff {} {
 
 	if {$GIT_COMMITTER_IDENT == {}} {
 		if {[catch {set me [exec git var GIT_COMMITTER_IDENT]} err]} {
-			error_popup "Unable to obtain your identity:\n$err"
+			error_popup "Unable to obtain your identity:\n\n$err"
 			return
 		}
 		if {![regexp {^(.*) [0-9]+ [-+0-9]+$} \
 			$me me GIT_COMMITTER_IDENT]} {
-			error_popup "Invalid GIT_COMMITTER_IDENT:\n$me"
+			error_popup "Invalid GIT_COMMITTER_IDENT:\n\n$me"
 			return
 		}
 	}