added utility function urljoin_keep_path
Allow users to query a list of coordinates

Due to restrictions by the SDSS server it can be useful to query a list
of coordinates in a single query. The result can then be matched with
the original list by using:

dr = coords.Angle(radius).to('degree').value
obj_coords = coords.SkyCoord(result['ra'], result['dec'], frame='icrs',
unit='deg')
matches, d2d, d3d = obj_coords.match_to_catalog_sky(pos)
result = result.group_by(matches)

where the group keys are the indices to the coordinates sent to the
query.

A future modification of astroquery can do the above procedure
automatically.
corrected missing brackets, units, and parenthesis
Changed SkyCoord to commons.CoordClasses
use six library for Py3 compatibility
adjusted documentation for utils.url_helpers.urljoin_keep_path to latest changes
break lines after 74 chars in docstring
Merge branch 'master' of github.com:astropy/astroquery into urlutil
Merge pull request #373 from derdon/urlutil

added utility function urljoin_keep_path
Changed check for scalar
Merge pull request #376 from fred3m/SDSS-batch-query

Allow users to query a list of coordinates for SDSS query
irsa_dust.rst clarifications and addition of a link
ESO header schemae didn't allow lists-of-strings because of an incorrect
call
Merge pull request #379 from keflavich/eso-header-schema

ESO header schema: minor fix
State dependency versions more clearly
Merge pull request #321 from cdeil/issue_321

Unicode encoding error on Python 3.2
IRSA dust coordinates parsing
minor typo
use transform_to everywhere
attempt to fix failing tests by monkeypatching: this is probably deeply
wrong