make: stop on errors or continue

["Mark M. Ito" <marki@jlab.org>]

I just checked in some changes that will allow us to choose whether or 
not make stops on errors or continues on. If you give the -k option to 
GNU make, then it will continue on even if errors are encountered. This 
will work recursively, i. e., the -k switch will be passed on to 
sub-makes. If you omit the -k switch, then an error will terminate the make.

The changes are part of revision 2910 of the trunk/src tree.