go rework

This commit includes:
* a new go package that uses gccgo to bootstrap the go toolchain
* env support added to Executable
* a new Go fetch strategy that uses `go get` to fetch a package and all
  of its deps
* A platinum searcher package that leverages the new go package and
  fetch strategy

lib/spack/spack/fetch_strategy.py

@@ -381,6 +381,60 @@ def __str__(self):
     def __repr__(self):
         return "%s<%s>" % (self.__class__, self.url)
 
+class GoFetchStrategy(VCSFetchStrategy):
+    """Fetch strategy that employs the `go get` infrastructure
+       Use like this in a package:
+
+           version('name', go='github.com/monochromegane/the_platinum_searcher/...')
+
+       Go get does not natively support versions, they can be faked with git
+    """
+    enabled = True
+    required_attributes = ('go',)
+
+    def __init__(self, **kwargs):
+        # Discards the keywords in kwargs that may conflict with the next call to __init__
+        forwarded_args = copy.copy(kwargs)
+        forwarded_args.pop('name', None)
+
+        super(GoFetchStrategy, self).__init__('go', **forwarded_args)
+        self._go = None
+
+    @property
+    def go_version(self):
+        vstring = self.go('version', output=str).split(' ')[2]
+        return Version(vstring)
+
+    @property
+    def go(self):
+        if not self._go:
+            self._go = which('go', required=True)
+        return self._go
+
+    @_needs_stage
+    def fetch(self):
+        self.stage.chdir()
+
+        tty.msg("Trying to get go resource:", self.url)
+
+        try:
+            os.mkdir('go')
+        except OSError:
+            pass
+        env = dict(os.environ)
+        env['GOPATH'] = os.path.join(os.getcwd(),'go')
+	self.go('get', '-v', '-d', self.url, env=env)
+
+    def archive(self, destination):
+        super(GoFetchStrategy, self).archive(destination, exclude='.git')
+
+    @_needs_stage
+    def reset(self):
+        self.stage.chdir_to_source()
+        self.go('clean')
+
+    def __str__(self):
+        return "[go] %s" % self.url
 
 class GitFetchStrategy(VCSFetchStrategy):
     """Fetch strategy that gets source code from a git repository.

lib/spack/spack/util/executable.py

@@ -105,6 +105,8 @@ def __call__(self, *args, **kwargs):
         fail_on_error = kwargs.pop("fail_on_error", True)
         ignore_errors = kwargs.pop("ignore_errors", ())
 
+	env = kwargs.get('env', None)
+
         # TODO: This is deprecated.  Remove in a future version.
         return_output = kwargs.pop("return_output", False)
 
@@ -149,7 +151,7 @@ def streamify(arg, mode):
 
         try:
             proc = subprocess.Popen(
-                cmd, stdin=istream, stderr=estream, stdout=ostream)
+                cmd, stdin=istream, stderr=estream, stdout=ostream, env=env)
             out, err = proc.communicate()
 
             rc = self.returncode = proc.returncode