Fix assumption that StringStream.peek returns a string
Fix assumption that StringStream.peek returns a string

Closes #776

femhub/CodeMirror2,filonb/CodeMirror2,filonb/CodeMirror2,femhub/CodeMirror2,femhub/CodeMirror2,leoshine/CodeMirror,filonb/CodeMirror2,leoshine/CodeMirror