Add test cases for partial downloading.
Add test cases for partial downloading.

blt/lhttpc,esl/fusco,cs-codesocial/lhttpc,hukl/lhttpc,waisbrot/lhttpc,whisper1/lhttpc,ferd/lhttpc,lpgauth/lhttpc,SiftLogic/lhttpc,talko/lhttpc,spilgames/lhttpc,hirotnk/lhttpc,Licenser/lhttpc