BUG: Fixed object type missmatch in SymLogNorm

Currently SymLogNorm accepts both linthresh and vmin, vmax with their
native dtype, meaning that the contents of one object cannot be updated
with another due to a mismatch of types.
ENH better error message when wrong cmap name.

Now prints all possible choices
Update scatter_demo.py

colors added
Merge pull request #2494 from ugurthemaster/master

Update scatter_demo.py
Merge remote-tracking branch 'upstream/v1.3.x'

Conflicts:
	lib/matplotlib/__init__.py
	setup.py
Fix build
Adding a missing 'b' back into two 'bbox_' kwargs

Got lost in commit fad3bc1f432e7dac8a18cdd99dae65178dda8f17
Merge pull request #2496 from androomerrill/inset_locator_fix

Adding a missing 'b' back into two 'bbox_' kwargs
add failing test: savefig(StringIO(), format="ps")
Merge pull request #2428 from cpelley/symlognorm_fix

BUG: Fixed object type missmatch in SymLogNorm
BUG: Fixed object type missmatch in SymLogNorm

Currently SymLogNorm accepts both linthresh and vmin, vmax with their
native dtype, meaning that the contents of one object cannot be updated
with another due to a mismatch of types.
Merge remote-tracking branch 'upstream/v1.3.x'
Merge pull request #2491 from pelson/pep8_re-enable

Re-enabled PEP8 test, closing #2443.
Merge pull request #2485 from NelleV/error_message

ENH better error message when wrong cmap name.
add new ps backend test file in `__init__.py`
Fix writing to all manner of StringIO-like objects in PS backend.
Merge pull request #2512 from mdboom/ps_StringIO

Fix saving to in-memory file-like objects in Postscript backend
Fix encoding issues when font name contains non-ascii characters
Minor doc fixes
Merge pull request #2523 from mdboom/ps-unicode-error

Unicode issue in EPS output when using custom font