Update INSTALL.

Add a note about failing "make check". The source of
the problem should be fixed in libtool (if it really is
a libtool bug and not mine) but I'm unable to spend time
on that for now. Thanks to Nelson H. F. Beebe for reporting
the issue.

Add a note about a possible need to run "ldconfig" after
"make install".
Build: Add --disable-doc to configure.
Build: Fix the combination of --disable-xzdec --enable-lzmadec.

In this case "make install" could fail if the man page directory
didn't already exist at the destination. If it did exist, a
dangling symlink was created there. Now the link is omitted
instead. This isn't the best fix but it's better than the old
behavior.