Add Expect package (#3517)

* Add Expect package

* Ignore patches during flake8 tests for package.py files

* Remove controversial changes

var/spack/repos/builtin/packages/tcl/package.py

@@ -55,6 +55,13 @@ def setup_environment(self, spack_env, run_env):
         run_env.set('TCL_LIBRARY', join_path(self.prefix.lib, 'tcl{0}'.format(
             self.spec.version.up_to(2))))
 
+    def install(self, spec, prefix):
+        with working_dir(self.build_directory):
+            make('install')
+
+            # Some applications like Expect require private Tcl headers.
+            make('install-private-headers')
+
     @run_after('install')
     def symlink_tclsh(self):
         with working_dir(self.prefix.bin):