ARROW-394: [Integration] Generate tests cases for numeric types, strings, lists, structs

Automatically generating testing files from Python.

Author: Wes McKinney <wes.mckinney@twosigma.com>

Closes apache#219 from wesm/ARROW-394 and squashes the following commits:

7807f48 [Wes McKinney] OS X doesn't have std::fabs
c0c804c [Wes McKinney] abs -> fabs
8cd1902 [Wes McKinney] Fix compiler warning in OS X from incorrect type declaration
d51581a [Wes McKinney] Add missing apache license
527622d [Wes McKinney] ARROW-414: remove check for maximum buffer padding
2a7b0fc [Wes McKinney] Add JSON generation code to fuzz test numeric types, print integers more nicely. Add integration tests to Travis CI build matrix. Add ApproxEquals method for floating point comparisons. Add boolean, string, struct, list to generated json test case

Author: wesm

vector/src/main/java/org/apache/arrow/vector/BaseDataValueVector.java

@@ -30,9 +30,6 @@ public abstract class BaseDataValueVector extends BaseValueVector implements Buf
 
   protected final static byte[] emptyByteArray = new byte[]{}; // Nullable vectors use this
 
-  /** maximum extra size at the end of the buffer */
-  private static final int MAX_BUFFER_PADDING = 64;
-
   public static void load(ArrowFieldNode fieldNode, List<BufferBacked> vectors, List<ArrowBuf> buffers) {
     int expectedSize = vectors.size();
     if (buffers.size() != expectedSize) {
@@ -51,9 +48,6 @@ public static void truncateBufferBasedOnSize(List<ArrowBuf> buffers, int bufferI
     if (buffer.writerIndex() < byteSize) {
       throw new IllegalArgumentException("can not truncate buffer to a larger size " + byteSize + ": " + buffer.writerIndex());
     }
-    if (buffer.writerIndex() - byteSize > MAX_BUFFER_PADDING) {
-      throw new IllegalArgumentException("Buffer too large to resize to " + byteSize + ": " + buffer.writerIndex());
-    }
     buffer.writerIndex(byteSize);
   }