`system' return code not (portably) interpretable

[Andreas Rottmann]

The integer returned by the 'system' procedure is not (portably) interpretable by Scheme code (in C it as to be destructured by the WIFEXITED() macro & co.):

    Ikarus Scheme version 0.0.4-rc1+, 64-bit (revision 1746, build 2009-03-01)
    Copyright (c) 2006-2008 Abdulaziz Ghuloum

    > (system "exit 1")
    256

As there is already code to interpret that integer for implementing `wstatus-exit-code' and `wstatus-received-signal', this functionality should probably refactored to expose a procedure to destructure the return value of `system' as well.