update rails to 3.2.20

This is a security fix against a file existence exposure CVE-2014-7819

see:
http://weblog.rubyonrails.org/2014/10/30/Rails_3_2_20_4_0_11_4_1_7_and_4_2_0_beta3_have_been_released/

Conflicts:
	Gemfile.lock
Fix sprockets file exposure vulnerability

There is an information leak vulnerability in Sprockets. This
vulnerability
has been assigned the CVE identifier CVE-2014-7819.

see:
https://groups.google.com/forum/#!topic/rubyonrails-security/wQBeGXqGs3E

The patch given in
https://15028051456732132684.googlegroups.com/attach/7887e1a7070ca526/2-12-sec-static-files.patch?part=0.0.1&view=1&vt=ANaJVrGrEs8fNpWjOUFuf3p1rWA83Dw-kPMJ8qeYExCi_n6nnuHcw53a2rWDfBwsfeA06s9Okm3LkpBK1W_b0vsqlsNAHGW1g0Z0T8WcmWxvqJCshdVpLts

Was manually applied to the backport branch.

This commit can be reverted as soon as sprockets 2.12.X is used.