Starting with version 2.0, the `pyproj.pyproj_datadir` constant was deprecated in favor of the `pyproj.datadir.get_data_dir()` constant.
A minor alteration to Basemap's `__init__.py` file allows compatibility with both the newer and older versions of pyproj regarding this breaking change.

Since version 2.0, pyproj comes with an internal data directory that is used in favor of the one set by the PROJ_LIB environment variable (or, on Linux, of the default proj folder set by PROJ.4). It appears this internal directory sometimes does not contain the epsg file (at least on Linux), which may however be found by looking up those other locations.

This commit therefore adds attempts to look up for the epsg file when it cannot be found in pyproj's internal datadir.

FileNotFoundError is not part of built-in exceptions in Python 2.
This commit allows to use it in Python 3, and replace it with a
RuntimeError in Python 2.

TODO: add license file regarding epsg, based
on terms of use, which are found here:
http://www.epsg.org/TermsOfUse.aspx

Source: https://github.com/OSGeo/proj.4/blob/5.2/nad/epsg