Release calc version 2.10.2t30

help/interrupt

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+Interrupts
+
+    While a calculation is in progress, you can generate the SIGINT
+    signal, and the calculator will catch it.  At appropriate points
+    within a calculation, the calculator will check that the signal
+    has been given, and will abort the calculation cleanly.  If the
+    calculator is in the middle of a large calculation, it might be
+    a while before the interrupt has an effect.
+
+    You can generate the SIGINT signal multiple times if necessary,
+    and each time the calculator will abort the calculation at a more
+    risky place within the calculation.  Each new interrupt prints a
+    message of the form:
+
+	    [Abort level n]
+
+    where n ranges from 1 to 3.  For n equal to 1, the calculator will
+    abort calculations at the next statement boundary.  For n equal to 2,
+    the calculator will abort calculations at the next opcode boundary.
+    For n equal to 3, the calculator will abort calculations at the next
+    lowest level arithmetic operation boundary.
+
+    If a final interrupt is given when n is 3, the calculator will
+    immediately abort the current calculation and longjmp back to the
+    top level command level.  Doing this may result in corrupted data
+    structures and unpredictable future behavior, and so should only
+    be done as a last resort.  You are advised to quit the calculator
+    after this has been done.