elfcopy: exclude extension when converting from binary

[emaste]

Summary

When converting from binary to ELF, elfcopy creates symbols _binary_<filename>_start_, _binary_<filename>_end, and _binary_<filename>_size. For compatibility with GNU objcopy (and to produce sensible symbol names) the extension must be stripped off.

[imp]

looks good to me. At least one test I ran with this a few weeks ago worked.