P/santoch/cr/script issues

@apond - please review
Fixed crasher when javascript file was not found in the zip package; Added USAGE message SCP_10 to note when epub3 has scripting in use; Ensured SCP_004 is emitted when a javascript file is found in the document, and that its entry is marked as scripted;  Added location data to SCP_004 messages; Changed SCP_004 context info to maximum 60 characters instead of the whole script (which became unreadable)