raise_if_conflicts

I noticed some conflicts with middleman-pagination-1.1.0 after installing middleman-core-3.3.2. They were triggered whenever I tried to run "middleman" commands outside an already installed middleman instance. For example:

```
10:28:43 ~/Sites $ middleman init middleman
/Users/bryan.braun/.rbenv/versions/1.9.3-p429/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:1999:in `raise_if_conflicts': Unable to activate middleman-pagination-1.1.0, because middleman-core-3.3.2 conflicts with middleman-core (~> 3.2.0) (Gem::LoadError)
	from /Users/bryan.braun/.rbenv/versions/1.9.3-p429/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:1237:in `activate'
	from /Users/bryan.braun/.rbenv/versions/1.9.3-p429/lib/ruby/site_ruby/1.9.1/rubygems.rb:194:in `rescue in try_activate'
	from /Users/bryan.braun/.rbenv/versions/1.9.3-p429/lib/ruby/site_ruby/1.9.1/rubygems.rb:191:in `try_activate'
	from /Users/bryan.braun/.rbenv/versions/1.9.3-p429/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:132:in `rescue in require'
	from /Users/bryan.braun/.rbenv/versions/1.9.3-p429/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:144:in `require'
	from /Users/bryan.braun/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/middleman-core-3.3.2/lib/middleman-core/extensions.rb:68:in `block in load_extensions_in_path'
	from /Users/bryan.braun/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/middleman-core-3.3.2/lib/middleman-core/extensions.rb:67:in `each'
	from /Users/bryan.braun/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/middleman-core-3.3.2/lib/middleman-core/extensions.rb:67:in `load_extensions_in_path'
	from /Users/bryan.braun/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/middleman-core-3.3.2/lib/middleman-core/load_paths.rb:40:in `setup_load_paths'
	from /Users/bryan.braun/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/middleman-core-3.3.2/bin/middleman:10:in `<top (required)>'
	from /Users/bryan.braun/.rbenv/versions/1.9.3-p429/bin/middleman:23:in `load'
	from /Users/bryan.braun/.rbenv/versions/1.9.3-p429/bin/middleman:23:in `<main>'
```

I didn't have these issues, when I was running on middleman 3.2.0. I ended up uninstalling the middleman-pagination since I wasn't actively using it, and the issue was resolved.

It's possible this is just some dependency issue that I'm not managing properly, but I figured I'd flag it for you, just in case.