Avoid start_loop keyword in Bokeh 0.12.4

[mrocklin]

No description provided.

[heroxbd]

This might not be correct. bokeh.__versoin__ is conda_version instead of bokeh version.

for bokeh-0.12.4,

import bokeh; print bokeh.__version__
0.11.1

But the follow works,

python -c 'from bokeh import _version; print _version.version_version'
0.12.4

[heroxbd]

Also the string comparison does not work for 0.9.7:
bokeh.__version__ <= '0.12.3'

python -c 'print "0.9.7" <= "0.12.3"'
False