Add option to skip the CTRL-C prompt

[anonymous]

The CTRL-C prompt is really annoying for Sage (or potentially other software interfacing with Singular):

                     SINGULAR                                 /  Development
 A Computer Algebra System for Polynomial Computations       /   version 3-1-3
                                                           0<
 by: W. Decker, G.-M. Greuel, G. Pfister, H. Schoenemann     \   March 2011
FB Mathematik der Universitaet, D-67653 Kaiserslautern        \
> ^C// ** Interrupt at cmd:`$INVALID$` in line:';'
abort command(a), continue(c) or quit Singular(q) ?

The attached patch adds a command-line option --cntrlc=CHAR which skips the CTRL-C prompt and automatically answers CHAR. i.e. running Singular using

Singular --cntrlc=a

will always "abort" on CTRL-C.

[hannes]

fixed as proposed, but without a new global variable