Convert Python 2 idioms to Python 2/3-compatible ones.

- convert print, StringIO, except as, octals, izip
- convert print statement to print function
- convert StringIO to six.StringIO
  - remove usage of csv reader in Spec, in favor of simple regex
  - csv reader only does byte strings
- convert 0755 octal literals to 0o755
- convert `except Foo, e` to `except Foo as e`
- fix a few places `str` is used.
  - may need to switch everything to str later.
- convert iteritems usages to use six.iteritems
- fix urllib and HTMLParser
- port metaclasses to use six.with_metaclass
- More octal literal conversions for Python 2/3
- Fix a new octal literal.
- Convert `basestring` to `six.string_types`
- Convert xrange -> range
- Fix various issues with encoding, iteritems, and Python3 semantics.
- Convert contextlib.nested to explicitly nexted context managers.
- Convert use of filter() to list comprehensions.
- Replace reduce() with list comprehensions.
-  Clean up composite: replace inspect.ismethod() with callable()
- Python 3 doesn't have "method" objects; inspect.ismethod returns False.
- Need to use callable in Composite to make it work.
- Update colify to use future division.
- Fix zip() usages that need to be lists.
- Python3: Use line-buffered logging instead of unbuffered.
- Python3 raises an error with unbuffered I/O
  - See https://bugs.python.org/issue17404

bin/spack

@@ -24,6 +24,8 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
+from __future__ import print_function
+
 import sys
 if (sys.version_info[0] > 2) or (sys.version_info[:2] < (2, 6)):
     v_info = sys.version_info[:3]
@@ -74,8 +76,8 @@ for pyc_file in orphaned_pyc_files:
     try:
         os.remove(pyc_file)
     except OSError as e:
-        print ("WARNING: Spack may fail mysteriously. "
-               "Couldn't remove orphaned .pyc file: %s" % pyc_file)
+        print("WARNING: Spack may fail mysteriously. "
+              "Couldn't remove orphaned .pyc file: %s" % pyc_file)
 
 # If there is no working directory, use the spack prefix.
 try: