Add all xcode versions supported by Travis to testing.

.travis.yml

@@ -29,6 +29,21 @@ matrix:
     - env: TOOLSET=gcc-5.1
     - os: osx
       env: TOOLSET=xcode-6.1
+    - os: osx
+      env: TOOLSET=xcode-6.2
+      osx_image: beta-xcode6.2
+    - os: osx
+      env: TOOLSET=xcode-6.3
+      osx_image: beta-xcode6.3
+    - os: osx
+      env: TOOLSET=xcode-6.4
+      osx_image: xcode6.4
+    - os: osx
+      env: TOOLSET=xcode-7.0
+      osx_image: xcode7
+    - os: osx
+      env: TOOLSET=xcode-7.1
+      osx_image: xcode7.1
 
 before_install: wget "https://raw.githubusercontent.com/boostorg/regression/develop/ci/src/script.py"
 install: python script.py install