This is the continuation of the work Eric started for handling
"p_memsz > p_filesz" in arbitrary segments (rather than just the last,
BSS, segment). I've added the suggested changes:
- drop unused "elf_bss" variable
- report padzero() errors when PROT_WRITE is present
- refactor load_elf_interp() to use elf_load()
This passes my quick smoke tests, but I'm still trying to construct some
more complete tests...