PARQUET-1098: Install util/comparison.h

This was breaking third party builds. cc @majetideepak

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

Closes #395 from wesm/install-comparison-h and squashes the following commits:

42a48a8 [Wes McKinney] Install util/comparison.h
diff --git a/src/parquet/util/CMakeLists.txt b/src/parquet/util/CMakeLists.txt
index 4717266..7b13886 100644
--- a/src/parquet/util/CMakeLists.txt
+++ b/src/parquet/util/CMakeLists.txt
@@ -18,6 +18,7 @@
 # Headers: util
 install(FILES
   buffer-builder.h
+  comparison.h
   logging.h
   macros.h
   memory.h