Remove marketable_urls check from find_by_path_or_id.

When marketable_urls is false and only the path is passed, then neither
find_by_path nor find is triggered (ht @renechz).
Fix bug where user plugin order is reset each time user gets updated.
require a unique page part title scoped to this page only
fixes validation on the UI when creating a new page part with the same name as an existing part.
Made spec wording read as truthy.
Add note to changelog about #2282.
Reduce maintenance headache by allowing failures on rbx-19mode and jruby-19mode.
Require at least Ruby 1.9.3 and thus drop Ruby 1.8.x support.
Remove all 1.8 modes from CI.
Document #2277 in changelog
Add note to changelog about #2278 and #2281.
Tiny update for Getting Started guide.
Update link in changelog.
About time for 2.0.10

Conflicts:
	changelog.md
Documented solution to #2236

Conflicts:
	changelog.md
Update getting started guide.
Dynamically set attr_accessible for all defined SeoMeta attributes.
Move wymeditor docs to be at the same place as the code itself.
Temp solution to fix failing specs.

I've tried countless stub variations but to no avail. When these two
specs run they change I18n settings and thus cause failure in
subsequent specs which are unrelated. Still looking for proper fix...