Ignore non-ascii chars in extracted PDF info.

I was seeing a few of these errors.


#<ArgumentError: invalid byte sequence in US-ASCII>
/opt/local/lib64/ruby/gems/1.9.1/gems/docsplit-0.6.3/lib/docsplit/info_extractor.rb:24:in `match'
/opt/local/lib64/ruby/gems/1.9.1/gems/docsplit-0.6.3/lib/docsplit/info_extractor.rb:24:in `match'
/opt/local/lib64/ruby/gems/1.9.1/gems/docsplit-0.6.3/lib/docsplit/info_extractor.rb:24:in `extract'
(eval):3:in `extract_length'
/opt/local/lib64/ruby/gems/1.9.1/gems/docsplit-0.6.3/lib/docsplit/image_extractor.rb:34:in `convert'
/opt/local/lib64/ruby/gems/1.9.1/gems/docsplit-0.6.3/lib/docsplit/image_extractor.rb:19:in `block (3 levels) in extract'
/opt/local/lib64/ruby/gems/1.9.1/gems/docsplit-0.6.3/lib/docsplit/image_extractor.rb:19:in `each'
/opt/local/lib64/ruby/gems/1.9.1/gems/docsplit-0.6.3/lib/docsplit/image_extractor.rb:19:in `block (2 levels) in extract'
/opt/local/lib64/ruby/gems/1.9.1/gems/docsplit-0.6.3/lib/docsplit/image_extractor.rb:18:in `each'
/opt/local/lib64/ruby/gems/1.9.1/gems/docsplit-0.6.3/lib/docsplit/image_extractor.rb:18:in `each_with_index'
/opt/local/lib64/ruby/gems/1.9.1/gems/docsplit-0.6.3/lib/docsplit/image_extractor.rb:18:in `block in extract'
/opt/local/lib64/ruby/gems/1.9.1/gems/docsplit-0.6.3/lib/docsplit/image_extractor.rb:16:in `each'
/opt/local/lib64/ruby/gems/1.9.1/gems/docsplit-0.6.3/lib/docsplit/image_extractor.rb:16:in `extract'
/opt/local/lib64/ruby/gems/1.9.1/gems/docsplit-0.6.3/lib/docsplit.rb:58:in `extract_images'


It turns out the problem was the metadata returned from pdfinfo  contained the restricted symbol (R) in some of the fields.

For example:
Creator:        Microsoft® Office Word 2007
Producer:       Microsoft® Office Word 2007
CreationDate:   Mon Jul 18 12:52:52 2011
ModDate:        Mon Jul 18 12:52:52 2011
Tagged:         yes
Pages:          4
Encrypted:      no
Page size:      612 x 792 pts (letter)
File size:      114279 bytes
Optimized:      no
PDF version:    1.5

After applying this patch to remove non-ascii characters from the pdfinfo output I was able to use docsplit.

Tested on Linux with ruby 1.9.1-p431 and 1.9.2-p0