AutotoolsPackage: minor improvements (#2859)

* AutotoolsPackage: added configure_directory to permit build out of source. The configure script executable is now invoked with an absolute path. Modified a few packages accordingly.

* build_systems: functions returning directories are now properties

* build_systems: fixed issues with tcl and tk

* AutotoolsPackage: reworked recipe for autoreconf

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

@@ -42,6 +42,8 @@ class Tcl(AutotoolsPackage):
 
     depends_on('zlib')
 
+    configure_directory = 'unix'
+
     def url_for_version(self, version):
         base_url = 'http://prdownloads.sourceforge.net/tcl'
         return '{0}/tcl{1}-src.tar.gz'.format(base_url, version)
@@ -52,9 +54,6 @@ def setup_environment(self, spack_env, env):
         env.set('TCL_LIBRARY', join_path(self.prefix.lib, 'tcl{0}'.format(
                 self.spec.version.up_to(2))))
 
-    def build_directory(self):
-        return 'unix'
-
     @run_after('install')
     def symlink_tclsh(self):
         with working_dir(self.prefix.bin):