BUG: Fix GeoSeries constructor for multi geoms

Because Multi* geometries are iterable, they get expanded when passed into
np.array(). Protect against this by passing in all base geometries as a
single element list. They will not be expanded into their individual
parts.

Switch on older versions of pandas when Series overrode __new__ instead
of __init__.
TST: Test GeoSeries constructor with index

Make sure that when a single geometry is passed in and the index contains
multiple elements, the geometry is replicated in the GeoSeries.

As suggested by @jtratner in Issue #70.
TST: Attempt to import unittest2 if running python 2.6
TST: Enable Travis CI for Python 2.6
BUG: Everybody likes dictionary comprehensions. Except Python 2.6.
TST: Clean up tests with assertRaises context manager.
TST: Separate python 2.6 requirements for Travis CI and add ordereddict
TST: pip install, don't source, the 2.6 requirements
BUG: OrderedDict is not in collections module in python 2.6
BUG: format statements need a position in python 2.6
TST: unittest2 didn't like skipIf
TST: Use local unittest for python 2.6 compatability in test_geocode
Revert "TST: unittest2 didn't like skipIf"

This reverts commit e70ea78321749b8229fdfd1b359b050af1c25a34.
TST: Use local unittest for python 2.6 compatability in test_types
TST: Explicitly use relative imports and clean up tests
DOC: Update docs to list supported python versions
BUG: Put back crs arguments that my merge had overwritten
Merge pull request #67 from kjordahl/test/python_2.6_support

Python 2.6 support
Merge pull request #70 from jwass/singlegeomfix

BUG: Fix GeoSeries constructor for multi geoms
PERF: Use faster version of list comprehension

Using index lookups is ~20% slower (and less pythonic) than unpacking
with comprehension. Plus use lazy iterator.