PARQUET-931: Add option to pin Arrow version with environment variable

Also added console output to show the version to help with debugging. I need this to help with pinning the Arrow version in conda-forge without necessarily making Arrow itself a build dependency (since it's cheap to build Arrow)

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

Closes #300 from wesm/PARQUET-931 and squashes the following commits:

0887958 [Wes McKinney] Do not build ARROW_IPC in thirdparty Arrow
98cae5a [Wes McKinney] Add option to pin Arrow version with $PARQUET_ARROW_VERSION environment variable. Upgrade default to current Arrow master
diff --git a/cmake_modules/ThirdpartyToolchain.cmake b/cmake_modules/ThirdpartyToolchain.cmake
index 30e4bab..f573cf4 100644
--- a/cmake_modules/ThirdpartyToolchain.cmake
+++ b/cmake_modules/ThirdpartyToolchain.cmake
@@ -372,9 +372,16 @@
     -DCMAKE_C_FLAGS=${CMAKE_C_FLAGS}
     -DCMAKE_INSTALL_PREFIX=${ARROW_PREFIX}
     -DARROW_JEMALLOC=OFF
+    -DARROW_IPC=OFF
     -DARROW_BUILD_TESTS=OFF)
 
-  set(ARROW_VERSION "c2f28cd07413e262fa0b741c286f86d5c7277c56")
+  if ("$ENV{PARQUET_ARROW_VERSION}" STREQUAL "")
+    set(ARROW_VERSION "bb8514cc9d7068c8b62d346577370751d68221d8")
+  else()
+    set(ARROW_VERSION "$ENV{PARQUET_ARROW_VERSION}")
+  endif()
+  message(STATUS "Building Apache Arrow from commit: ${ARROW_VERSION}")
+
   set(ARROW_URL "https://github.com/apache/arrow/archive/${ARROW_VERSION}.tar.gz")
 
   if (CMAKE_VERSION VERSION_GREATER "3.2")