Bug 1010028 - Set args properly for various debuggers. r=glandium

Set args properly to to separate the debugger and process arguments.
Also add "--args" automatically for gdb front-end cgdb and ddd.

Verification Steps:
1. mach debug +debugger gdb
2. Make sure gdb is launched correctly.
Bug 1006695 - Mark JS worker threads to be known by Nuwa. r=khuey

They will be recreated in the spawned process.
Bug 1006695 - Mark workers in thread pool to be known by Nuwa. r=khuey

They will be recreated in the spawned process.
Bug 998076 - implement responseURL attribute for XMLHttpRequest. r=smaug