fixes for exception handling; added system.compileOption

tests/accept/run/tcontinuexc.nim

@@ -0,0 +1,21 @@
+type
+  ESomething = object of E_Base
+  ESomeOtherErr = object of E_Base
+
+proc genErrors(s: string) =
+  if s == "error!":
+    raise newException(ESomething, "Test")
+  else:
+    raise newException(EsomeotherErr, "bla")
+
+try:
+  for i in 0..3:
+    try:
+      genErrors("error!")
+    except ESomething:
+      echo("Error happened")
+    echo "came here"
+    raise newException(EsomeotherErr, "bla")
+finally:  
+  echo "caught"
+

tests/accept/run/toverflw2.nim

@@ -0,0 +1,5 @@
+var a : int32 = 2147483647
+var b : int32 = 2147483647
+var c = a + b
+
+