Introduce option 'on_error'
The option on_error defines the behaviour of isl in case of an error.
By default, the option is set to 'warn'. This is the current behaviour
and means isl prints a warning and continues the execution of the
program. We also introduce two new modes: 'continue' and 'abort'.
'continue' does not print any warning, but continues execution and 'abort'
abort the program from within isl. 'abort' is useful for debuggers as
they automatically break at the place of the error condition.
Signed-off-by: Tobias Grosser <tobias@grosser.es>
Signed-off-by: Sven Verdoolaege <skimo@kotnet.org>