Cannot plot a simple map over Africa if lon_0 is not equal to zero

This might be related to https://github.com/matplotlib/basemap/issues/183
I have a quite simple global 0.1 degree image that I would like to put onto a map. The code for reproducing the problem is the following.
```python
m = Basemap(width=12000000, height=8000000,
resolution='l', projection='stere',
lat_ts=0, lat_0=0, lon_0=21.)
# m = Basemap(width=9000000, height=9000000,
# projection='aeqd', lat_0=0, lon_0=1)
lons = np.arange(-179.95, 180.01, 0.1)
lats = np.arange(-89.95, 90.01, 0.1)
data = np.random.random((1800, 3600))
lons, lats = np.meshgrid(lons, lats)
x, y = m(lons, lats)
m.pcolormesh(x, y, data,
latlon=False, cmap='RdBu')
# m.imshow(np.flipud(anom)[1500:2470,600:1200])
m.drawcoastlines()
m.drawcountries()
plt.show()
```
The result is the following:

Changing `lon_0` from 21 to 0 gives the following:

I've also tried this with `aeqd` and `laea` projections with the same results.

##### conda environment for testing
```
name: test_basemap
channels:
- !!python/unicode
'defaults'
- !!python/unicode
'conda-forge'
dependencies:
- !!python/unicode
'basemap=1.0.7=np112py27_0'
- !!python/unicode
'cairo=1.14.8=0'
- !!python/unicode
'cycler=0.10.0=py27_0'
- !!python/unicode
'dbus=1.10.10=0'
- !!python/unicode
'expat=2.1.0=0'
- !!python/unicode
'fontconfig=2.12.1=3'
- !!python/unicode
'freetype=2.5.5=2'
- !!python/unicode
'functools32=3.2.3.2=py27_0'
- !!python/unicode
'geos=3.5.0=0'
- !!python/unicode
'glib=2.50.2=1'
- !!python/unicode
'gst-plugins-base=1.8.0=0'
- !!python/unicode
'gstreamer=1.8.0=0'
- !!python/unicode
'icu=54.1=0'
- !!python/unicode
'jpeg=9b=0'
- !!python/unicode
'libffi=3.2.1=1'
- !!python/unicode
'libgcc=5.2.0=0'
- !!python/unicode
'libiconv=1.14=0'
- !!python/unicode
'libpng=1.6.27=0'
- !!python/unicode
'libxcb=1.12=1'
- !!python/unicode
'libxml2=2.9.4=0'
- !!python/unicode
'matplotlib=2.0.0=np112py27_0'
- !!python/unicode
'mkl=2017.0.1=0'
- !!python/unicode
'numpy=1.12.1=py27_0'
- !!python/unicode
'openssl=1.0.2k=1'
- !!python/unicode
'pcre=8.39=1'
- !!python/unicode
'pip=9.0.1=py27_1'
- !!python/unicode
'pixman=0.34.0=0'
- !!python/unicode
'pycairo=1.10.0=py27_0'
- !!python/unicode
'pyparsing=2.1.4=py27_0'
- !!python/unicode
'pyqt=5.6.0=py27_2'
- !!python/unicode
'python=2.7.13=0'
- !!python/unicode
'python-dateutil=2.6.0=py27_0'
- !!python/unicode
'pytz=2016.10=py27_0'
- !!python/unicode
'qt=5.6.2=3'
- !!python/unicode
'readline=6.2=2'
- !!python/unicode
'setuptools=27.2.0=py27_0'
- !!python/unicode
'sip=4.18=py27_0'
- !!python/unicode
'six=1.10.0=py27_0'
- !!python/unicode
'sqlite=3.13.0=0'
- !!python/unicode
'subprocess32=3.2.7=py27_0'
- !!python/unicode
'tk=8.5.18=0'
- !!python/unicode
'wheel=0.29.0=py27_0'
- !!python/unicode
'zlib=1.2.8=3'
prefix: !!python/unicode '/home/cpa/.pyenv/versions/miniconda-3.16.0/envs/test_basemap'
```

Start by running the provided Basemap reproduction with the listed Python, matplotlib, and numpy environment, comparing lon_0=21 with lon_0=0 and the aeqd and laea examples. No source files or tests are named; done means the global pcolormesh is correctly positioned over the map for nonzero lon_0 values without breaking the other projections.

Written by the indexing model from the issue text.