Fix various typos in source documentation and comments (cont.)

Found via `codespell`

misc/MacQetDeploy.sh

@@ -43,7 +43,7 @@ echo "This script :"
 echo "\t - up date the svn depot"
 echo "\t - built the application bundle,"
 echo "\t - copy over required Qt frameworks,"
-echo "\t - copy additionnal files: translations, titleblocks and elements,"
+echo "\t - copy additional files: translations, titleblocks and elements,"
 echo "\t - create image disk."
 echo
 echo "Enjoy ;-)"
@@ -93,7 +93,7 @@ if [ -e "build-aux/mac-osx/${APPNAME} $tagName r$HEAD.dmg" ] ; then
     read userinput
     if  [ "$userinput" == "n" ] ; then
         echo
-        echo "Process is stoped."
+        echo "Process is stopped."
         echo
         exit
     fi

misc/launch_qet.sh

@@ -12,7 +12,7 @@ QET_LANG_DIR=$(readlink -f "${current_dir}/../lang/")
 
 # checks for the qelectrotech binary executable file
 if [ ! -x "${QET_EXE}" ]; then
-	echo "Errror : executable file not found. Aborting."
+	echo "Error : executable file not found. Aborting."
 	exit 1
 fi