I went through the textfile and was able to get RMagick to make
thumbnails again! The only problem is it fails a bunch of the post
install tests.

They all pretty much look like this:
post-setup.rb: setting up documentation...
/usr/bin/ruby -I /Users/pj/Desktop/RMagick-1.8.1/lib -I
/Users/pj/Desktop/RMagick-1.8.1/ext/RMagick InitialCoords.rb
/Users/pj/Desktop/RMagick-1.8.1/lib/rvg/misc.rb:320:in `render':
undefined method `width' for nil:NilClass (NoMethodError)
        from /Users/pj/Desktop/RMagick-1.8.1/lib/rvg/misc.rb:688:in
`text'
        from /Users/pj/Desktop/RMagick-1.8.1/lib/rvg/text.rb:64:in
`add_primitives'
        from /Users/pj/Desktop/RMagick-1.8.1/lib/rvg/container.rb:71:in
`add_primitives'
        from /Users/pj/Desktop/RMagick-1.8.1/lib/rvg/container.rb:71:in
`each'
        from /Users/pj/Desktop/RMagick-1.8.1/lib/rvg/container.rb:71:in
`add_primitives'
        from /Users/pj/Desktop/RMagick-1.8.1/lib/rvg/rvg.rb:262:in
`add_outermost_primitives'
        from /Users/pj/Desktop/RMagick-1.8.1/lib/rvg/rvg.rb:262:in
`each'
        from /Users/pj/Desktop/RMagick-1.8.1/lib/rvg/rvg.rb:262:in
`add_outermost_primitives'
        from /Users/pj/Desktop/RMagick-1.8.1/lib/rvg/rvg.rb:235:in
`draw'
        from InitialCoords.rb:23
post-setup.rb: InitialCoords.rb example returned error code 256