Revert "git-gui: remove lines starting with the comment character"

This reverts commit b9a43869c9.

This commit causes breakage on macOS (10.13). It causes errors on
startup and completely breaks the commit functionality. There are two
main problems. First, it uses `string cat` which is not supported on
older Tcl versions. Second, it does a half close of the bidirectional
pipe to git-stripspace which is also not supported on older Tcl
versions.

Reported-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Pratyush Yadav <me@yadavpratyush.com>

lib/commit.tcl

@@ -141,20 +141,6 @@ proc setup_commit_encoding {msg_wt {quiet 0}} {
 	}
 }
 
-proc strip_msg {msg} {
-	set cmd [concat [list | ] [_git_cmd stripspace] --strip-comments]
-	_trace_exec $cmd
-	set fd [open $cmd r+]
-	fconfigure $fd -translation binary -encoding utf-8
-
-	puts -nonewline $fd $msg
-	close $fd w
-	set result [read $fd]
-	close $fd
-
-	return $result
-}
-
 proc commit_tree {} {
 	global HEAD commit_type file_states ui_comm repo_config
 	global pch_error
@@ -221,8 +207,8 @@ You must stage at least 1 file before you can commit.
 
 	# -- A message is required.
 	#
-	set msg [strip_msg [$ui_comm get 1.0 end]]
-
+	set msg [string trim [$ui_comm get 1.0 end]]
+	regsub -all -line {[ \t\r]+$} $msg {} msg
 	if {$msg eq {}} {
 		error_popup [mc "Please supply a commit message.