Changed default assignment of shorcut for alt-left/right to history next/prev, which is more standard and useful.

Indent can be done with tab and shift-tab anyway.
If you don't like this, feel free to reassign them manually in the editor settings :P

tools/editor/plugins/script_editor_plugin.cpp

@@ -2091,8 +2091,8 @@ ScriptEditor::ScriptEditor(EditorNode *p_editor) {
 	file_menu->get_popup()->add_shortcut(ED_SHORTCUT("script_editor/reload_script_soft", TTR("Soft Reload Script"), KEY_MASK_CMD|KEY_MASK_SHIFT|KEY_R), FILE_TOOL_RELOAD_SOFT);
 	file_menu->get_popup()->add_separator();
 
-	file_menu->get_popup()->add_shortcut(ED_SHORTCUT("script_editor/history_previous", TTR("History Prev"), KEY_MASK_CTRL|KEY_MASK_ALT|KEY_LEFT), WINDOW_PREV);
-	file_menu->get_popup()->add_shortcut(ED_SHORTCUT("script_editor/history_next", TTR("History Next"), KEY_MASK_CTRL|KEY_MASK_ALT|KEY_RIGHT), WINDOW_NEXT);
+	file_menu->get_popup()->add_shortcut(ED_SHORTCUT("script_editor/history_previous", TTR("History Prev"), KEY_MASK_ALT|KEY_LEFT), WINDOW_PREV);
+	file_menu->get_popup()->add_shortcut(ED_SHORTCUT("script_editor/history_next", TTR("History Next"), KEY_MASK_ALT|KEY_RIGHT), WINDOW_NEXT);
 	file_menu->get_popup()->add_separator();
 	file_menu->get_popup()->add_shortcut(ED_SHORTCUT("script_editor/import_theme", TTR("Import Theme")), FILE_IMPORT_THEME);
 	file_menu->get_popup()->add_shortcut(ED_SHORTCUT("script_editor/reload_theme", TTR("Reload Theme")), FILE_RELOAD_THEME);

tools/editor/plugins/script_text_editor.cpp

@@ -1206,8 +1206,8 @@ void ScriptTextEditor::register_editor() {
 	ED_SHORTCUT("script_text_editor/select_all", TTR("Select All"), KEY_MASK_CMD|KEY_A);
 	ED_SHORTCUT("script_text_editor/move_up", TTR("Move Up"), KEY_MASK_ALT|KEY_UP);
 	ED_SHORTCUT("script_text_editor/move_down", TTR("Move Down"), KEY_MASK_ALT|KEY_DOWN);
-	ED_SHORTCUT("script_text_editor/indent_left", TTR("Indent Left"), KEY_MASK_ALT|KEY_LEFT);
-	ED_SHORTCUT("script_text_editor/indent_right", TTR("Indent Right"), KEY_MASK_ALT|KEY_RIGHT);
+	ED_SHORTCUT("script_text_editor/indent_left", TTR("Indent Left"), 0);
+	ED_SHORTCUT("script_text_editor/indent_right", TTR("Indent Right"), 0);
 	ED_SHORTCUT("script_text_editor/toggle_comment", TTR("Toggle Comment"), KEY_MASK_CMD|KEY_K);
 	ED_SHORTCUT("script_text_editor/clone_down", TTR("Clone Down"), KEY_MASK_CMD|KEY_B);
 #ifdef OSX_ENABLED