install doesnt work on osx atm - adding conditions suggested by this …

…blog post: nodejs/node-gyp#26

binding.gyp

@@ -7,6 +7,13 @@
       'include_dirs': ['/usr/local/include', "./"],
       'cflags_cc!': ['-fno-rtti', '-fno-exceptions'],
       'cflags_cc+': ['-frtti', '-fexceptions'],
+      'conditions': [
+        ['OS=="mac"', {
+          'xcode_settings': {
+            'GCC_ENABLE_CPP_RTTI': 'YES'
+          }
+        }]
+      ],
       'link_settings': {
         'ldflags': ['-L/usr/local/lib'],
         'libraries': ['/usr/local/lib/libavrocpp.so']