Convert #resolve_for into an iterative algorithm (for profit)
Comments and warning fixes
Added multiple argument handling to gem list
Refactored to Gem Query
Finishing Query touches
fix Gem::Specification to always return files in a predictably sorted order
suppress list source header if only one type requested with --quiet
Use metadata['allowed_push_host'] to restrict gem pushing to that host only . Defaults to nil, meaning any host is allowed. Includes tests.

Note that I had to change 2 tests in test_gem_commands_push_command.rb, namely test_execute and test_execute_host; they exploited the fact that gem push previously did not always attempt to load a gem's specification (it only loaded the gemspec if no host was specified). I used existing test helpers to fix those 2 tests.

I figure @rykov of @gemfury will appreciate this. Thanks to @drbrain for implementation suggestions.
Add full_require_paths.

Add convenient method, which returns expanded version of
require_paths. This removes code duplication and may helps #210 a bit.
Add 2.0.8 release notes to master
Add 1.8.26 release notes to History
Add 1.8.23.1 release notes to History
Add 2.0.9 release notes to History
Add missing "bug fixes" title to 2.0.9
Update the guides only when on master

Updating the guides makes no sense for work on a branch as only the
latest release should be featured in the guides.
Update the API documentation only on master

Updating the API for past releases only adds more work as it needs to
then be undone.
Merge pull request #603 from seamusabshere/allowed_hosts

Use metadata['allowed_push_host'] to restrict gem push to that host
Merge pull request #604 from zachrab/572_gem_list_multiple_args

gem list now lists results for multiple arguments
Update history for #603
Update history for #604