Have create_param() set the broadcast pattern

[f0k]

This PR makes create_param() set the broadcast pattern when creating a shared variable. We assume our network parameters never change shape, so we can at least fix the broadcast pattern (shared variables don't allow setting a fixed shape). This saves some headaches when users have a DenseLayer of 1 unit and try to do something fancy with the output (as here: https://groups.google.com/d/msg/lasagne-users/MQfjYI-tV2I/pf-z_NnyBQAJ), since now Theano can infer that the output is broadcastable on the last axis.

[coveralls]

Coverage remained the same at 100.0% when pulling f60389d on f0k:bcast-params into cf88e29 on Lasagne:master.

[benanne]

Sounds good, should we maybe have a comment in the code that explains why we are doing this (basically what you just said)? broadcastable patterns don't come up too often so it might baffle some people who read that piece of code.

[f0k]

Sounds good, should we maybe have a comment in the code that explains why we are doing this (basically what you just said)?

Good point, did that!

[coveralls]

Coverage remained the same at 100.0% when pulling 4d4e0b0 on f0k:bcast-params into cf88e29 on Lasagne:master.

[benanne]

LGTM, will merge soon if there are no further comments :)