Small ruby enhancement and tmuxinator package

It is currently less painful to pull the source from github, compile it into a
gem, then install the gem, than it is to download a gem and install it.  This
still lacks an activation mechanism, but `spack use tmuxinator` is functional.

lib/spack/spack/modules.py

@@ -130,6 +130,13 @@ def add_path(path_name, directory):
                 if site_packages:
                     add_path('PYTHONPATH', site_packages[0])
 
+            if self.spec.package.extends(spack.spec.Spec('ruby')):
+              add_path('GEM_PATH', self.spec.prefix)
+
+            # Allow module path extensions from packages
+            for key, val in self.spec.package.extra_environment:
+              add_path(key, val)
+
             # short description is just the package + version
             # TODO: maybe packages can optionally provide it.
             self.short_description = self.spec.format("$_ $@")

var/spack/packages/ruby/package.py

@@ -1,4 +1,6 @@
 from spack import *
+import spack
+import os
 
 class Ruby(Package):
     """A dynamic, open source programming language with a focus on 
@@ -7,6 +9,8 @@ class Ruby(Package):
     homepage = "https://www.ruby-lang.org/"
     url      = "http://cache.ruby-lang.org/pub/ruby/2.2/ruby-2.2.0.tar.gz"
 
+    extendable = True
+
     version('2.2.0', 'cd03b28fd0b555970f5c4fd481700852')
 
     def install(self, spec, prefix):
@@ -14,3 +18,24 @@ def install(self, spec, prefix):
 
         make()
         make("install")
+
+    def setup_dependent_environment(self, module, spec, ext_spec):
+        """Called before ruby modules' install() methods.  Sets GEM_HOME
+        and GEM_PATH to values appropriate for the package being built.
+
+        In most cases, extensions will only need to have one line::
+
+            gem('install', '<gem-name>.gem')
+        """
+        # Ruby extension builds have global ruby and gem functions
+        module.ruby = Executable(join_path(spec.prefix.bin, 'ruby'))
+        module.gem = Executable(join_path(spec.prefix.bin, 'gem'))
+
+        # Set GEM_PATH to include dependent gem directories
+        ruby_paths = []
+        for d in ext_spec.traverse():
+            if d.package.extends(self.spec):
+                ruby_paths.append(d.prefix)
+        os.environ['GEM_PATH'] = ':'.join(ruby_paths)
+        # The actual installation path for this gem
+        os.environ['GEM_HOME'] = ext_spec.prefix

var/spack/packages/tmuxinator/package.py

@@ -0,0 +1,17 @@
+from spack import *
+
+class Tmuxinator(Package):
+    """A session configuration creator and manager for tmux"""
+    homepage = "https://github.com/tmuxinator/tmuxinator"
+    url      = "https://github.com/tmuxinator/tmuxinator"
+
+    version('0.6.11', 
+        git='https://github.com/tmuxinator/tmuxinator',
+        tag='v0.6.11')
+
+    extends('ruby')
+
+    def install(self, spec, prefix):
+      gem('build', 'tmuxinator.gemspec')
+      gem('install', 'tmuxinator-{}.gem'.format(self.version))
+