Move C extension into the ext dir.

* Some versions of GNU install will error out if the install dir is the
  same as the build dir.
(cherry picked from commit bbf5f9ca0c3ae8fbe56ec2dd42def1d66d1c8ea2)

gpgme.gemspec

@@ -4,12 +4,12 @@ Gem::Specification.new do |s|
   s.authors           = ['Daiki Ueno']
   s.date              = '2011-05-09'
   s.email             = 'ueno@unixuser.org'
-  s.extensions        = ['extconf.rb']
+  s.extensions        = ['ext/gpgme/extconf.rb']
   s.files             = `git ls-files`.split("\n")
   s.has_rdoc          = true
   s.rubyforge_project = 'ruby-gpgme'
   s.homepage          = 'http://rubyforge.org/projects/ruby-gpgme/'
-  s.require_paths     = ['lib']
+  s.require_paths     = ['lib', 'ext']
   s.summary           = 'Ruby binding of GPGME.'
   s.description       = %q{Ruby-GPGME is a Ruby language binding of GPGME (GnuPG
 Made Easy). GnuPG Made Easy (GPGME) is a library designed to make access to