git-gui: Unify wording to say "to stage" instead of "to add"

Also, the warning message when clicking "Reset" is adapted to
the wording "Reset" rather than a confusion "Cancel commit?".

Signed-off-by: Christian Stimming <stimming@tuhh.de>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
diff --git a/git-gui.sh b/git-gui.sh
index f87b955..d7fad46 100755
--- a/git-gui.sh
+++ b/git-gui.sh
@@ -1827,12 +1827,12 @@
 	lappend disable_on_lock \
 		[list .mbar.commit entryconf [.mbar.commit index last] -state]
 
-	.mbar.commit add command -label {Add To Commit} \
+	.mbar.commit add command -label {Stage To Commit} \
 		-command do_add_selection
 	lappend disable_on_lock \
 		[list .mbar.commit entryconf [.mbar.commit index last] -state]
 
-	.mbar.commit add command -label {Add Tracked Files To Commit} \
+	.mbar.commit add command -label {Stage Changed Files To Commit} \
 		-command do_add_all \
 		-accelerator $M1T-I
 	lappend disable_on_lock \
@@ -2154,7 +2154,7 @@
 lappend disable_on_lock \
 	{.vpane.lower.commarea.buttons.rescan conf -state}
 
-button .vpane.lower.commarea.buttons.incall -text {Add Tracked} \
+button .vpane.lower.commarea.buttons.incall -text {Stage Changed} \
 	-command do_add_all
 pack .vpane.lower.commarea.buttons.incall -side top -fill x
 lappend disable_on_lock \
diff --git a/lib/checkout_op.tcl b/lib/checkout_op.tcl
index 40cc73a..170f737 100644
--- a/lib/checkout_op.tcl
+++ b/lib/checkout_op.tcl
@@ -248,7 +248,7 @@
 	if {[lock_index checkout_op]} {
 		after idle [cb _start_checkout]
 	} else {
-		_error $this "Index is already locked."
+		_error $this "Staging area (index) is already locked."
 		delete_this
 	}
 }
diff --git a/lib/commit.tcl b/lib/commit.tcl
index 1f5c2c3..f857a2f 100644
--- a/lib/commit.tcl
+++ b/lib/commit.tcl
@@ -153,7 +153,7 @@
 		U? {
 			error_popup "Unmerged files cannot be committed.
 
-File [short_path $path] has merge conflicts.  You must resolve them and add the file before committing.
+File [short_path $path] has merge conflicts.  You must resolve them and stage the file before committing.
 "
 			unlock_index
 			return
@@ -169,7 +169,7 @@
 	if {!$files_ready && ![string match *merge $curType]} {
 		info_popup {No changes to commit.
 
-You must add at least 1 file before you can commit.
+You must stage at least 1 file before you can commit.
 }
 		unlock_index
 		return
diff --git a/lib/index.tcl b/lib/index.tcl
index 3ea72e1..f47f929 100644
--- a/lib/index.tcl
+++ b/lib/index.tcl
@@ -360,7 +360,7 @@
 		"[appname] ([reponame])" \
 		"Revert changes in $s?
 
-Any unadded changes will be permanently lost by the revert." \
+Any unstaged changes will be permanently lost by the revert." \
 		question \
 		1 \
 		{Do Nothing} \
diff --git a/lib/merge.tcl b/lib/merge.tcl
index 148d859..f6a2df3 100644
--- a/lib/merge.tcl
+++ b/lib/merge.tcl
@@ -45,7 +45,7 @@
 
 File [short_path $path] has merge conflicts.
 
-You must resolve them, add the file, and commit to complete the current merge.  Only then can you begin another merge.
+You must resolve them, stage the file, and commit to complete the current merge.  Only then can you begin another merge.
 "
 			unlock_index
 			return 0
@@ -219,16 +219,20 @@
 	if {![lock_index abort]} return
 
 	if {[string match *merge* $commit_type]} {
-		set op merge
+		set op_question "Abort merge?
+
+Aborting the current merge will cause *ALL* uncommitted changes to be lost.
+
+Continue with aborting the current merge?"
 	} else {
-		set op commit
+		set op_question "Reset changes?
+
+Resetting the changes will cause *ALL* uncommitted changes to be lost.
+
+Continue with resetting the current changes?"
 	}
 
-	if {[ask_popup "Abort $op?
-
-Aborting the current $op will cause *ALL* uncommitted changes to be lost.
-
-Continue with aborting the current $op?"] eq {yes}} {
+	if {[ask_popup $op_question] eq {yes}} {
 		set fd [git_read read-tree --reset -u HEAD]
 		fconfigure $fd -blocking 0 -translation binary
 		fileevent $fd readable [namespace code [list _reset_wait $fd]]