Return warning if extension doesn't match content type
Add test for correct extension, but incorrect content-type
Only check against text/csv
Merge branch 'master' of github.com:theodi/csvlint.rb into feature-detect-file-extension

Conflicts:
	lib/csvlint.rb
Merge branch 'master' of github.com:theodi/csvlint.rb into feature-detect-file-extension

Conflicts:
	csvlint.gemspec
Merge pull request #10 from theodi/feature-detect-file-extension

Return warning if extension doesn't match content type