Improve OS X codesign information on failure

hooks/after_install_codesign

@@ -13,9 +13,15 @@
   # Require 10.7 - FIXME: Should be 10.7 or newer.
   [[ "$(/usr/bin/sw_vers -productVersion)" == 10.7* ]] || return 2
 
+  # Find out ruby executable to sign
+  typeset _ruby_name
+  _ruby_name="$(sed -n '/^ruby_install_name=/ {s/ruby_install_name="\(.*\)"/\1/; p; };' "$MY_RUBY_HOME/config" )"
+
   # Require rvm_codesign_identity
   [[ -n "${rvm_codesign_identity:-}" ]] || {
-    rvm_warn "'rvm_codesign_identity' is not set, please set it in ~/.rvmrc"
+    rvm_warn "'rvm_codesign_identity' is not set so RVM can't sign ${_ruby_name}\n" \
+             "Set it in ~/.rvmrc after reading the following about OS X code signing:\n" \
+             "https://developer.apple.com/library/mac/#documentation/Security/Conceptual/CodeSigningGuide/Introduction/Introduction.html"
     return 3
   }
 
@@ -25,10 +31,6 @@
     return 4
   }
 
-  # Find out ruby executable to sign
-  typeset _ruby_name
-  _ruby_name="$(sed -n '/^ruby_install_name=/ {s/ruby_install_name="\(.*\)"/\1/; p; };' "$MY_RUBY_HOME/config" )"
-
   # Sign ruby
   /usr/bin/codesign -f -s "${rvm_codesign_identity}" "$(which "${_ruby_name}")"
 )