Support binary wave version 7 (wave names longer than 31 characters) #32

Igor Pro 8+ saves any wave whose name exceeds 31 bytes as binary-wave version 7. igor2 0.5.15 cannot parse these. Inside a .pxp, packed.load fails on the record, so the wave is lost.

Layout, observed in .pxp files from Igor Pro 9:

The header and body are identical to version 5, except that the version field is 7.
The 32-byte bname field in WaveHeader5 holds the placeholder :wave name too long:.
The BinHeader5 field at offset 56 (optionsSize1 in v5) holds the length of the long name.
The long name, not NUL-terminated, follows the last v5 section (after sIndices), and ends the record.
Example: r_ReactedQ_1p73Inlet_0006_270_30 (32 bytes). The field at offset 56 is 32, and the record ends with those 32 bytes.

Parsing v7 as v5 and replacing bname with that trailing name gives correct data and names in our tests. This follows #28 / #30, which fixed long folder names (record type 101). I can provide a test experiment.