reset intraFrames in jsmpeg constructor
reset intraFrames in jsmpeg constructor

fix #93 by initialising intraFrames property in jsmpeg constructor
fixes seekToFrame behaviour when loading more than one video

faljse/jsmpeg,faljse/jsmpeg,phoboslab/jsmpeg,faljse/jsmpeg,phoboslab/jsmpeg,phoboslab/jsmpeg,phoboslab/jsmpeg