MFC r210324, r210438.

MFC r210324, r210438.

r210324:
  - Correctly handle sections of type SHT_NOBITS.  For these sections:
    - elf_getdata() and elf_rawdata() should return an "Elf_Data" structure
      that has its "d_buf" member set to NULL and "d_size" member set to
      the nominal 'size' of the section.
    - Update the manual page for these functions.
  - Fix a memory leak in an error handling path inside elf_getdata().
  - Use _libelf_allocate_data() in elf_newdata() for consistency.

r210438: (np)
  Catch up with r210324.  d_buf will be NULL for SHT_NOBITS sections, do not
  attempt to copy from it in that case.

git-svn-id: svn://svn.freebsd.org/base/stable/8@212198 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f