The breaking change is here: http://git.yoctoproject.org/cgit.cgi/poky/commit/bitbake/lib/bb/fetch2/perforce.py?id=094742bed2fc01d55f572da946fcfa7a48521401

The author of the patch misunderstood the code; the split() was not intended to break the file stream into lines; it was intended to split a single line at whitespace for some p4-specific formatting. 

The 'for file in p4file:' line is what split the stream into lines, since iterating over a file handle yields lines, but now it is broken due to operating on a string instead of a file stream handle.

A possible fix would be something to the effect of 'for file in p4file.splitlines():' or on an earlier line, 'p4file = p4file.splitlines()'.  I added a change like this and it fixed it for me.