Issue 7657: Scripts list freezes the browser with very long "javascript:" url

https://code.google.com/p/fbug/issues/detail?id=7657
Fixed test case for issue 3652
Fixed test for issue 5400
Removed test case for issue 7300 as watch expressions are not cropped
since issue 7591
Allow circumventing the cropping of POST bodies by allowing to set
extensions.firebug.netDisplayedPostBodyLimit to 0
Merge remote-tracking branch 'origin/master' into issue7655