Fix rubygems hook execution when gemspec.rdoc_options contains --ri

[tompng]

Probably fixes #1343

options.finish is called twice while generating document through rubygems_hook.
If gemspec has spec.rdoc_options << '--ri', document generation fails.
Looks like this double-finish is introduced in #1274

Detail of the bug

options = ::RDoc::Options.new
options.parse args # if --ri is specified, generator is set to 'ri'
options.finish # @template='ri' and @template_dir=nil is configured here
@rdoc.parse_files options.files

document 'ri', options, @rdoc_dir
document 'darkfish', options, @rdoc_dir # Calls options.setup_generator('darkfish') and options.finish but @template_dir is already configured for 'ri'

Fix

Constraints are:

• Need to call finish only once for each RDoc::Options instance
• finish should be called before rdoc.parse_files(options.files)
• finish should be called after options.setup_generator
• It is better to call rdoc.parse_files only once

We need to use a different RDoc::Options object for parse_files phase and document generation phase.

[kou]

+1

[kou]

How about adding a comment why we need to create a separated options here?