zsh: make the disabling of /etc optional

Library/Formula/zsh.rb

@@ -10,20 +10,35 @@ class Zsh < Formula
 
   skip_clean :all
 
+  def disable_etcdir?
+    ARGV.include? '--disable-etcdir'
+  end
+
+  def options
+    [
+      ['--disable-etcdir', 'Disable the reading of Zsh rc files in /etc'],
+    ]
+  end
+
   def install
-    system "./configure", "--prefix=#{prefix}",
-                          "--disable-etcdir",
-                          "--enable-fndir=#{share}/zsh/functions",
-                          "--enable-site-fndir=#{share}/zsh/site-functions",
-                          "--enable-scriptdir=#{share}/zsh/scripts",
-                          "--enable-site-scriptdir=#{share}/zsh/site-scripts",
-                          "--enable-cap",
-                          "--enable-function-subdirs",
-                          "--enable-maildir-support",
-                          "--enable-multibyte",
-                          "--enable-pcre",
-                          "--enable-zsh-secure-free",
-                          "--with-tcsetpgrp"
+    args = [
+      "-prefix=#{prefix}",
+      "--enable-fndir=#{share}/zsh/functions",
+      "--enable-site-fndir=#{share}/zsh/site-functions",
+      "--enable-scriptdir=#{share}/zsh/scripts",
+      "--enable-site-scriptdir=#{share}/zsh/site-scripts",
+      "--enable-cap",
+      "--enable-function-subdirs",
+      "--enable-maildir-support",
+      "--enable-multibyte",
+      "--enable-pcre",
+      "--enable-zsh-secure-free",
+      "--with-tcsetpgrp"
+    ]
+
+    args << '--disable-etcdir' if disable_etcdir?
+
+    system "./configure", *args
 
     # Do not version installation directories.
     inreplace ["Makefile", "Src/Makefile"],
@@ -38,6 +53,15 @@ def test
 
   def caveats; <<-EOS.undent
     To use this build of Zsh as your login shell, add it to /etc/shells.
+
+    If you have administrator privileges, you must fix an Apple miss
+    configuration in Mac OS X 10.7 Lion by renaming /etc/zshenv to
+    /etc/zprofile, or Zsh will have the wrong PATH when executed
+    non-interactively by scripts.
+
+    Alternatively, install Zsh with /etc disabled:
+
+      brew install --disable-etcdir zsh
     EOS
   end
 end