3.4.1 Script compatibility before release 0.5

In order to conform final SRFI-22, Gauche release 0.5.1 changes the way main is called. Unfortunately, this makes the Scheme scripts that is written for older Gauche no longer work. I decided to take this change now, in the early stage of Gauche, rather than keeping incomatibility to the standard (srfi).

The incompatible changes are these two points.

• The argument list passed to main now includes the script name itself as the first element. In older version, only the arguments after the script file name are passed.
• When main returns non-integral value, gosh exits with code 70. In older version, gosh exits with code 0 in such case.