declare and initialize new provate members in jsdScript, copy important script properties at jsdScript creation time, so they're around after Invalidate().
add onForRuntime() method to jsdIDebuggerService to let native code turn on the deubgger (on() can only be called from js)
register an app-start observer so we can turn on the debugger at startup if "js.debugger.autostart" pref is true.
r=peterv, bug 81840
move from pc as a ulong to pc as an object wrapped around a uword
relocate jsdService constructor to jsd_xpp.cpp in order to initialize the global
service