add mac wheels for 10.9 / 64b only

* update multibuild to support building osx 10.9 / 64b only wheels
* make 10.9 builds the default
* move override of pandas MACOSX_DEPLOYEMENT_TARGET from .travis.yml to config.sh

Author: robbuckley

.travis.yml

@@ -5,6 +5,7 @@ env:
       - BUILD_COMMIT=v0.24.2
       - PLAT=x86_64
       - UNICODE_WIDTH=32
+      - MB_PYTHON_OSX_VER=10.9
       - NP_BUILD_DEP="numpy==1.12.1"
       - NP_TEST_DEP="numpy==1.12.1"
       - WHEELHOUSE_UPLOADER_USERNAME=travis-worker
@@ -62,18 +63,15 @@ matrix:
       language: generic
       env:
         - MB_PYTHON_VERSION=2.7
-        - MACOSX_DEPLOYMENT_TARGET=10.6 # since pandas PR24274, mac builds default to 10.9
     - os: osx
       language: generic
       env:
         - MB_PYTHON_VERSION=3.5
-        - MACOSX_DEPLOYMENT_TARGET=10.6 # since pandas PR24274, mac builds default to 10.9
+        - MB_PYTHON_OSX_VER=10.6 # no python.org 10.9 builds for 3.5
     - os: osx
       language: generic
       env:
         - MB_PYTHON_VERSION=3.6
-        - MACOSX_DEPLOYMENT_TARGET=10.6 # since pandas PR24274, mac builds default to 10.9
-
 
 before_install:
     # See:

config.sh

@@ -4,7 +4,15 @@
 function pre_build {
     # Any stuff that you need to do before you start building the wheels
     # Runs in the root directory of this repository.
-    :
+    if [ -n "$IS_OSX" ]; then
+        # Override pandas' default minimum MACOSX_DEPLOYEMENT_TARGET=10.9,
+        # so we can build for older Pythons if we really want to.
+        # See https://github.com/pandas-dev/pandas/pull/24274
+        local _plat=$(get_distutils_platform)
+        if [[ -z $MACOSX_DEPLOYMENT_TARGET && "$_plat" =~ macosx-(10\.[0-9]+)-.* ]]; then
+            export MACOSX_DEPLOYMENT_TARGET=${BASH_REMATCH[1]}
+        fi
+    fi
 }
 
 function build_wheel {