Fix segfault when incrementing whole vector values.

Also removed RefExpr::Eval(Val*) method since it was never called
(Clang emitted warning about this hiding overloaded virtual function
UnaryExpr::Eval(Frame*)) and doesn't appear to be necessary even if it
was called to avoid the default vector handling of UnaryExpr::Eval
(as the comment suggests as the intention).

testing/btest/Baseline/language.incr-vec-expr/out

@@ -0,0 +1,5 @@
+[0, 0, 0]
+[a=0, b=test, c=[1, 2, 3]]
+[1, 1, 1]
+[a=1, b=test, c=[1, 2, 3]]
+[a=1, b=test, c=[2, 3, 4]]

testing/btest/core/leaks/incr-vec-expr.test

@@ -0,0 +1,35 @@
+# Needs perftools support.
+#
+# @TEST-REQUIRES: bro  --help 2>&1 | grep -q mem-leaks
+#
+# @TEST-GROUP: leaks
+#
+# @TEST-EXEC: HEAP_CHECK_DUMP_DIRECTORY=. HEAPCHECK=local bro -b -m -r $TRACES/chksums/ip4-udp-good-chksum.pcap %INPUT
+
+type rec: record {
+    a: count;
+    b: string;
+    c: vector of count;
+};
+
+global vec: vector of count = vector(0,0,0);
+
+global v: rec = [$a=0, $b="test", $c=vector(1,2,3)];
+
+event new_connection(c: connection)
+    {
+    print vec;
+    print v;
+
+    ++vec;
+
+    print vec;
+
+    ++v$a;
+
+    print v;
+
+    ++v$c;
+
+    print v;
+    }

testing/btest/language/incr-vec-expr.test

@@ -0,0 +1,27 @@
+# @TEST-EXEC: bro -b %INPUT >out
+# @TEST-EXEC: btest-diff out
+
+type rec: record {
+    a: count;
+    b: string;
+    c: vector of count;
+};
+
+global vec: vector of count = vector(0,0,0);
+
+global v: rec = [$a=0, $b="test", $c=vector(1,2,3)];
+
+print vec;
+print v;
+
+++vec;
+
+print vec;
+
+++v$a;
+
+print v;
+
+++v$c;
+
+print v;