Fix 'chsh' by checking '/etc/shells' instead of using 'which'

fix test for chsh in install
in case $SHELL is zsh but not the last one in /etc/shells
fixes #3026 fixes #3779 fixes #3780

tools/install.sh

@@ -32,10 +32,12 @@ sed -i -e "/export PATH=/ c\\
 export PATH=\"$PATH\"
 " ~/.zshrc
 
-if [ "$SHELL" != "$(which zsh)" ]; then
+TEST_CURRENT_SHELL=$(expr "$SHELL" : '.*/\(.*\)')
+if [ "$TEST_CURRENT_SHELL" != "zsh" ]; then
     echo "\033[0;34mTime to change your default shell to zsh!\033[0m"
-    chsh -s `which zsh`
+    chsh -s $(grep /zsh$ /etc/shells | tail -1)
 fi
+unset TEST_CURRENT_SHELL
 
 echo "\033[0;32m"'         __                                     __   '"\033[0m"
 echo "\033[0;32m"'  ____  / /_     ____ ___  __  __   ____  _____/ /_  '"\033[0m"