Fix incremental index updates

Initialize Gem::Specification in the same way when incrementally
updating indexes as in a full reindex.

Fixes https://github.com/rubygems/rubygems/issues/232
Add test case demonstrating update_index failure

Extend test_gem_indexer to better reflect system state in update_index.
Fix missing load_yaml in YAML-related requirement.rb code.
Fix error on creating a Version object with a frozen string.
Merge pull request #370 from jruby/backport_yaml_fix

Fix missing load_yaml in YAML-related requirement.rb code.
Merge pull request #380 from jruby/version_init_error_frozen_string

Fix error on creating a Version object with a frozen string.
Gem.load_yaml is called from Gem::Specification.from_yaml, this line can
be deleted.
Merge pull request #389 from tenderlove/1.8

Gem.load_yaml can be removed
Merge pull request #364 from whitepages/fix_update_index

- Fixed incremental index updates (#232)
- Specification#ruby_code didn't handle Requirement with multiple
  values correctly. Fixes required_rubygems_version w/ upper and lower
  bound.
Bump to 1.8.25
Upload then publish_docs since publish_docs fails sometimes