Use require_relative to prevent encoding.rb from being loaded twice

[shanebonham]

Ever since 2c321b2, I get this warning when loading up a console session:

/usr/local/Cellar/rbenv/0.4.0/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/prawn-0.13.1/lib/prawn/encoding.rb:12:
warning: already initialized constant CHARACTERS

From what I can tell, this happens because prawn.rb now uses require_relative to load in the rest of the library. When it loads prawn/font, prawn/font/afm gets required, which in turn requires prawn/encoding. Next, prawn.rb loads prawn/encoding, which should be ignored, because it's already loaded, but what I find is that, for me, locally, require loads encoding.rb from /usr/local/opt/rbenv/{etc}, while require_relative loads it from /usr/local/Cellar/rbenv/{etc}.

These are the same files (I'm using rbenv and homebrew), but it seems like ruby doesn't realize that and tries to load both. This commit switches the require in afm.rb to use require_relative, which resolves the issue for me.

If there is an alternate way to resolve this, perhaps at a config level on just my system, I am all ears!

[practicingruby]

This is fine, we want to switch to using requre_relative throughout the project now that 1.8 is no longer a concern. Will merge next time I'm working on stuff.

[practicingruby]

Thanks again Shane, this has been merged into stable and will go out in a 0.13.2 release next Monday.

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[practicingruby]

There were other files that were generating warnings too. Took care of those in 3f36909.