Fix typo in testing documentation
Merge pull request #943 from Sinjo/fix_test_docs_typo

Fix typo in testing documentation
Numerous fixes for StringIO in 1.9 mode.

Much of the logic here for 1.9 mode is now a nearly-direct port of
the MRI logic. This should bring us closer to supporting encoding
properly for the key StringIO operations like read and gets.
Merge remote-tracking branch 'origin/master'
More faithful port of strio_read.
Rename "data" to "ptr" to more closely match MRI source.
Additional minor tweaks to get StringIO closer to 100%.