Fix ConstantEvaluator to correctly handle single element tuples.

test/libsolidity/syntaxTests/arrayLength/inline_array.sol

@@ -0,0 +1,5 @@
+contract C {
+    uint[[2]] a15;
+}
+// ----
+// TypeError: (22-25): Invalid array length, expected integer literal or constant expression.

test/libsolidity/syntaxTests/arrayLength/parentheses.sol

@@ -0,0 +1,25 @@
+contract C {
+    uint constant L1 = (2);
+    uint constant L2 = ((2));
+    uint constant L3 = ((((2))));
+    uint constant L4 = (2 + 1);
+    uint constant L5 = ((2 + 1));
+    uint constant L6 = (((2) + ((1))));
+    uint constant L7 = (2 + 1) / 1;
+    uint constant L8 = (2 + ((1))) / (1);
+    uint[L1] a1;
+    uint[L2] a2;
+    uint[L3] a3;
+    uint[L4] a4;
+    uint[L5] a5;
+    uint[L6] a6;
+    uint[L7] a7;
+    uint[L8] a8;
+    uint[(2)] a9;
+    uint[(2 + 1)] a10;
+    uint[(2 + 1) + 1] a11;
+    uint[((2) + 1) + 1] a12;
+    uint[(2 + 1) + ((1))] a13;
+    uint[(((2) + 1)) + (((1)))] a14;
+    uint[((((2) + 1)) + (((1))))%1] a15;
+}

test/libsolidity/syntaxTests/arrayLength/tuples.sol

@@ -0,0 +1,5 @@
+contract C {
+    uint[(1,2)] a15;
+}
+// ----
+// TypeError: (22-27): Invalid array length, expected integer literal or constant expression.