Request #30296:  Motif error browser needs buttons.

The error browser is now easier to use due to the addition of three
action buttons for repeating the last evaluation (Repeat), editing the
source (Edit), and closing the window (Close).  This change applies to
all platforms.


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Request #50076:  Closing projects with invalid source path.

The problem here was that after multiple error browsers were opened
and closed, MLWorks would then crash in various ways.  To test this,
in the Listener, invoke the error browser several times, killing it in
between, and then exit MLWorks.  There should be no fatal signal error
message which appeared before.