build: add correct shared library naming on OS X

The build system currently creates a shared library on OS X with the
same name as on Linux i.e.  libnode.so.48.  This is inconsistent with
the conventions on OS X which uses libnode.48.so This commit changes
the build process and install.py (used by make binary) to build with
the correct name on OS X when the --shared configure parameter is used.

PR-URL: https://github.com/nodejs/node/pull/7687
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

tools/install.py

@@ -118,10 +118,11 @@ def files(action):
     if is_windows:
       output_file += '.dll'
     else:
-      # GYP will output to lib.target, this is hardcoded in its source,
-      # see the _InstallableTargetInstallPath function.
-      output_prefix += 'lib.target/'
-      output_file = 'lib' + output_file + '.so.' + get_version()
+      output_file = 'lib' + output_file + '.' + variables.get('shlib_suffix')
+      # GYP will output to lib.target except on OS X, this is hardcoded
+      # in its source - see the _InstallableTargetInstallPath function.
+      if sys.platform != 'darwin':
+        output_prefix += 'lib.target/'
 
   action([output_prefix + output_file], 'bin/' + output_file)