Displays the previous version of the gem when run bundle update

Change code in the 3 source files to display the method locked_gems in
lib/bundler.rb

Add 3 Rspec test in the update directory for each source: rubygems, git,
path.
Put old version message in the  block level

Change bundle update message format

Change rspec bundle update message text to match in files (rubygem, git, path
source, etc)
fix raising error when path contains unexisting users home dir
Added the message 'Could not locate Gemfile' to the GemfileNotFound exception raised by Bundler::Settings#[]=.
By doing this, users who just run 'bundle' in the wrong directory will see a friendly message instead of just "Bundle::GemfileNotFound".
fix error message and test
Merge pull request #2639 from joyicecloud/show-version-of-gem-updated

Displays the previous version of the gem when run bundle update

Conflicts:
	lib/bundler/source.rb
	lib/bundler/source/git/git_proxy.rb
	lib/bundler/source/rubygems.rb
Deprecation message for when a gem's binstub is running another gem's bin.

closes #2659
Merge pull request #2689 from qblake/fix-path-with-unexisting-users-home-dir

fix raising error when path contains unexisting users home dir
friendlier error message
Add a rake task to update SSL Certificates.

Added a rake task under rubygems namespace that updates the SSL
certificates in bundler if they meet either of the following criteria:

a) The filenames do not match that of the certificates in Rubygems
   master
b) Rubygems contains an updated certificate
simplify the certs manager
update certs to match rubygems
certificate manager namespacing and path expansion
Merge pull request #2752 from DavidEGrayson/bundler_pull_request_1

Show something better than "Bundle::GemfileNotFound" when bundle is
run in the wrong directory.