Show backtrace during non fatal install steps if --debug

Library/Homebrew/install.rb

@@ -96,7 +96,7 @@ def install f
   rescue Exception => e
     opoo "The cleaning step did not complete successfully"
     puts "Still, the installation was successful, so we will link it into your prefix"
-    ohai e, e.inspect if ARGV.debug?
+    ohai e, e.backtrace if ARGV.debug?
     show_summary_heading = true
   end
 
@@ -122,11 +122,11 @@ def install f
   else
     begin
       Keg.new(f.prefix).link
-    rescue Exception
+    rescue Exception => e
       onoe "The linking step did not complete successfully"
       puts "The package built, but is not symlinked into #{HOMEBREW_PREFIX}"
       puts "You can try again using `brew link #{f.name}'"
-      ohai e, e.inspect if ARGV.debug?
+      ohai e, e.backtrace if ARGV.debug?
       show_summary_heading = true
     end
   end