BUG: Fix indexing 0-sized arrays using empty fancy-indexes

Due to subspace creation for fancy indexing selecting the 0s
element on every fancy dimension, this failed if the dimension
was empty. Propagating check_index to disable the unnecessary
check in this case.
ENH: Allow newaxis in combination with fancy indexing.

This commit allows the use of None when also using fancy indexing.
To achieve this mit->consec is used to note the denote the
transposition axis (which means that if its consecutive but at the
start, mit->consec==0, and no transposition is necessary).
BUG: Check for maximum dimension for fancy indexing.
BUG: Do not ignore subspace unless it is true 0-d

This is  more important when allowing newaxis, but already before
lead to successful indexing when it should not be suspected.
Also some maintenance.
MNT: Tiny cleanup for mapping.c and comments
TST: Add fancy indexing test for tuple indexing

This is a first version of fancy indexing tests by mimicing the
behavoir in python. Note that error messages are not tested.