Creating some (invalid) concatenated SFF files

This is to mimic a real SFF file created with the Roche software
version 2.6 (and perhaps post processed?) which concatenated
SFF files together (using different flow counts). Mimicking
this with invalid_greek_E3MFGYR02.sff (see below).

Furthermore, the expected 8 byte alignment was also broken -
the first SFF block in this example was only 4 byte aligned.
Mimicking this with invalid_paired_E3MFGYR02.sff (see below).

with open("E3MFGYR02_no_manifest.sff", "rb") as h:
    no_manifest = h.read()
with open("greek.sff", "rb") as h:
    greek = h.read()
with open("paired.sff", "rb") as h:
    paired = h.read()
assert paired[-4:] == chr(0) * 4
with open("invalid_greek_E3MFGYR02.sff", "wb") as h:
    h.write(greek + no_manifest)
with open("invalid_paired_E3MFGYR02.sff", "wb") as h:
    h.write(paired[:-4] + no_manifest + chr(0)*4)

Note that I have deliberately used the no manifest (and no index)
version of E3MFGYR02 here so we don't have to worry about if the
index offsets would be absolute or relative...

It is possible that this is a deliberate Roche design choice,
and a defacto extension to the SFF file format - we shall see.
Check for concatenated SFF files and treat as error

This is based on the following query (and test data file) from Matt:
http://www.biostars.org/p/80320/