Update fixnum to new package guidelines.

pkg/fixnum/lib/src/int64.dart

Index: pkg/fixnum/lib/src/int64.dart
diff --git a/pkg/fixnum/int64.dart b/pkg/fixnum/lib/src/int64.dart
similarity index 99%
rename from pkg/fixnum/int64.dart
rename to pkg/fixnum/lib/src/int64.dart
index 47ade3674b1e290f1b852a098a8b8c5645b8e9fb..cefb2c012a59e0b853324376746cf697917d9d83 100644
--- a/pkg/fixnum/int64.dart
+++ b/pkg/fixnum/lib/src/int64.dart
@@ -189,7 +189,7 @@ class int64 implements intx {
   }
 
   factory int64.fromBytes(List<int> bytes) {
-    int top = bytes[7] & 0xff; 
+    int top = bytes[7] & 0xff;
     top <<= 8;
     top |= bytes[6] & 0xff;
     top <<= 8;
@@ -197,7 +197,7 @@ class int64 implements intx {
     top <<= 8;
     top |= bytes[4] & 0xff;
 
-    int bottom = bytes[3] & 0xff; 
+    int bottom = bytes[3] & 0xff;
     bottom <<= 8;
     bottom |= bytes[2] & 0xff;
     bottom <<= 8;
@@ -209,7 +209,7 @@ class int64 implements intx {
   }
 
   factory int64.fromBytesBigEndian(List<int> bytes) {
-    int top = bytes[0] & 0xff; 
+    int top = bytes[0] & 0xff;
     top <<= 8;
     top |= bytes[1] & 0xff;
     top <<= 8;
@@ -217,7 +217,7 @@ class int64 implements intx {
     top <<= 8;
     top |= bytes[3] & 0xff;
 
-    int bottom = bytes[4] & 0xff; 
+    int bottom = bytes[4] & 0xff;
     bottom <<= 8;
     bottom |= bytes[5] & 0xff;
     bottom <<= 8;
@@ -458,7 +458,7 @@ class int64 implements intx {
     if (negative) {
       a2 += 0x3 << _BITS2; // add extra one bits on the left
     }
-    
+
     if (n < _BITS) {
       res2 = _shiftRight(a2, n);
       if (negative) {