add test for integer input

Integer input should be promoted to a floating point type. Check for
this. See issue #7.
transform3d: fix ext_mode==4 behaviour

The concatenation used for ext_mode==4 behaviour was incorrect.

TODO: check to see if this affect the inverse.
promote integer input to transform to floating point

Fixes #7.
Merge pull request #8 from rjw57/issue-7

promote integer input to transforms into floating point