In getObjectType(), doxygenify comment, and take a pointer to the

beginning of the archive member data as an argument.

Get rid of ParseLongFilenameSection(), which is dead.

In ReadArchiveBuffer(), implement support for 4.4BSD/MacOSX long filenames.
This is kind of invasive, because they prepend the long filename to the archive
member data, and then lie about the size. So we have to keep track of the real
size.

llvm-svn: 10392